diff --git a/src/aircraft_gui.cpp b/src/aircraft_gui.cpp
index ee2bf15ea3..ea04ffe4e8 100644
--- a/src/aircraft_gui.cpp
+++ b/src/aircraft_gui.cpp
@@ -120,6 +120,6 @@ void DrawAircraftImage(const Vehicle *v, const Rect &r, VehicleID selection, Eng
 		x += x_offs;
 		y += UnScaleGUI(rect.top) - heli_offs;
 		Rect hr = {x, y, x + width - 1, y + UnScaleGUI(rect.Height()) + heli_offs - 1};
-		DrawFrameRect(hr.Expand(WidgetDimensions::scaled.bevel), COLOUR_WHITE, FR_BORDERONLY);
+		DrawFrameRect(hr.Expand(WidgetDimensions::scaled.bevel), COLOUR_WHITE, FrameFlag::BorderOnly);
 	}
 }
diff --git a/src/genworld_gui.cpp b/src/genworld_gui.cpp
index 935404c445..4f347273db 100644
--- a/src/genworld_gui.cpp
+++ b/src/genworld_gui.cpp
@@ -1427,9 +1427,9 @@ struct GenerateProgressWindow : public Window {
 		switch (widget) {
 			case WID_GP_PROGRESS_BAR: {
 				/* Draw the % complete with a bar and a text */
-				DrawFrameRect(r, COLOUR_GREY, FR_BORDERONLY | FR_LOWERED);
+				DrawFrameRect(r, COLOUR_GREY, {FrameFlag::BorderOnly, FrameFlag::Lowered});
 				Rect br = r.Shrink(WidgetDimensions::scaled.bevel);
-				DrawFrameRect(br.WithWidth(br.Width() * _gws.percent / 100, _current_text_dir == TD_RTL), COLOUR_MAUVE, FR_NONE);
+				DrawFrameRect(br.WithWidth(br.Width() * _gws.percent / 100, _current_text_dir == TD_RTL), COLOUR_MAUVE, {});
 				SetDParam(0, _gws.percent);
 				DrawString(br.left, br.right, CenterBounds(br.top, br.bottom, GetCharacterHeight(FS_NORMAL)), STR_GENERATION_PROGRESS, TC_FROMSTRING, SA_HOR_CENTER);
 				break;
diff --git a/src/graph_gui.cpp b/src/graph_gui.cpp
index 7f14055e18..e9779cc656 100644
--- a/src/graph_gui.cpp
+++ b/src/graph_gui.cpp
@@ -611,7 +611,7 @@ public:
 					bool lowered = !HasBit(this->excluded_range, index);
 
 					/* Redraw frame if lowered */
-					if (lowered) DrawFrameRect(line, COLOUR_BROWN, FR_LOWERED);
+					if (lowered) DrawFrameRect(line, COLOUR_BROWN, FrameFlag::Lowered);
 
 					const Rect text = line.Shrink(WidgetDimensions::scaled.framerect);
 					DrawString(text, str, TC_BLACK, SA_CENTER, false, FS_SMALL);
@@ -1106,7 +1106,7 @@ struct PaymentRatesGraphWindow : BaseGraphWindow {
 			bool lowered = !HasBit(_legend_excluded_cargo_payment_rates, cs->Index());
 
 			/* Redraw frame if lowered */
-			if (lowered) DrawFrameRect(line, COLOUR_BROWN, FR_LOWERED);
+			if (lowered) DrawFrameRect(line, COLOUR_BROWN, FrameFlag::Lowered);
 
 			const Rect text = line.Shrink(WidgetDimensions::scaled.framerect);
 
@@ -1603,7 +1603,7 @@ struct IndustryProductionGraphWindow : BaseGraphWindow {
 			bool lowered = !HasBit(_legend_excluded_cargo_production_history, p.cargo);
 
 			/* Redraw frame if lowered */
-			if (lowered) DrawFrameRect(line, COLOUR_BROWN, FR_LOWERED);
+			if (lowered) DrawFrameRect(line, COLOUR_BROWN, FrameFlag::Lowered);
 
 			const Rect text = line.Shrink(WidgetDimensions::scaled.framerect);
 
diff --git a/src/misc_gui.cpp b/src/misc_gui.cpp
index ab685568cb..fcc02fb1f5 100644
--- a/src/misc_gui.cpp
+++ b/src/misc_gui.cpp
@@ -794,11 +794,11 @@ void QueryString::DrawEditBox(const Window *w, WidgetID wid) const
 	Rect cr = r.WithWidth(clearbtn_width, !rtl);
 	Rect fr = r.Indent(clearbtn_width, !rtl);
 
-	DrawFrameRect(cr, wi->colour, wi->IsLowered() ? FR_LOWERED : FR_NONE);
+	DrawFrameRect(cr, wi->colour, wi->IsLowered() ? FrameFlag::Lowered : FrameFlags{});
 	DrawSpriteIgnorePadding(rtl ? SPR_IMG_DELETE_RIGHT : SPR_IMG_DELETE_LEFT, PAL_NONE, cr, SA_CENTER);
 	if (StrEmpty(this->text.GetText())) GfxFillRect(cr.Shrink(WidgetDimensions::scaled.bevel), GetColourGradient(wi->colour, SHADE_DARKER), FILLRECT_CHECKER);
 
-	DrawFrameRect(fr, wi->colour, FR_LOWERED | FR_DARKENED);
+	DrawFrameRect(fr, wi->colour, {FrameFlag::Lowered, FrameFlag::Darkened});
 	GfxFillRect(fr.Shrink(WidgetDimensions::scaled.bevel), PC_BLACK);
 
 	fr = fr.Shrink(WidgetDimensions::scaled.framerect);
diff --git a/src/network/network_content_gui.cpp b/src/network/network_content_gui.cpp
index f55ee420a8..7adbbe077c 100644
--- a/src/network/network_content_gui.cpp
+++ b/src/network/network_content_gui.cpp
@@ -140,9 +140,9 @@ void BaseNetworkContentDownloadStatusWindow::DrawWidget(const Rect &r, WidgetID
 	switch (widget) {
 		case WID_NCDS_PROGRESS_BAR: {
 			/* Draw the % complete with a bar and a text */
-			DrawFrameRect(r, COLOUR_GREY, FR_BORDERONLY | FR_LOWERED);
+			DrawFrameRect(r, COLOUR_GREY, {FrameFlag::BorderOnly, FrameFlag::Lowered});
 			Rect ir = r.Shrink(WidgetDimensions::scaled.bevel);
-			DrawFrameRect(ir.WithWidth((uint64_t)ir.Width() * this->downloaded_bytes / this->total_bytes, _current_text_dir == TD_RTL), COLOUR_MAUVE, FR_NONE);
+			DrawFrameRect(ir.WithWidth((uint64_t)ir.Width() * this->downloaded_bytes / this->total_bytes, _current_text_dir == TD_RTL), COLOUR_MAUVE, {});
 			SetDParam(0, this->downloaded_bytes);
 			SetDParam(1, this->total_bytes);
 			SetDParam(2, this->downloaded_bytes * 100LL / this->total_bytes);
diff --git a/src/network/network_gui.cpp b/src/network/network_gui.cpp
index 72aa8e99e2..e497c90a91 100644
--- a/src/network/network_gui.cpp
+++ b/src/network/network_gui.cpp
@@ -1920,7 +1920,7 @@ public:
 			r.top = y + offset;
 			r.bottom = r.top + button->height - 1;
 
-			DrawFrameRect(r, button->colour, FR_NONE);
+			DrawFrameRect(r, button->colour, {});
 			DrawSprite(button->sprite, PAL_NONE, r.left + WidgetDimensions::scaled.framerect.left, r.top + WidgetDimensions::scaled.framerect.top);
 			if (button->disabled) {
 				GfxFillRect(r.Shrink(WidgetDimensions::scaled.bevel), GetColourGradient(button->colour, SHADE_DARKER), FILLRECT_CHECKER);
@@ -2094,7 +2094,7 @@ struct NetworkJoinStatusWindow : Window {
 		switch (widget) {
 			case WID_NJS_PROGRESS_BAR: {
 				/* Draw the % complete with a bar and a text */
-				DrawFrameRect(r, COLOUR_GREY, FR_BORDERONLY | FR_LOWERED);
+				DrawFrameRect(r, COLOUR_GREY, {FrameFlag::BorderOnly, FrameFlag::Lowered});
 				Rect ir = r.Shrink(WidgetDimensions::scaled.bevel);
 				uint8_t progress; // used for progress bar
 				switch (_network_join_status) {
@@ -2117,7 +2117,7 @@ struct NetworkJoinStatusWindow : Window {
 						progress = 15 + _network_join_bytes * (100 - 15) / _network_join_bytes_total;
 						break;
 				}
-				DrawFrameRect(ir.WithWidth(ir.Width() * progress / 100, _current_text_dir == TD_RTL), COLOUR_MAUVE, FR_NONE);
+				DrawFrameRect(ir.WithWidth(ir.Width() * progress / 100, _current_text_dir == TD_RTL), COLOUR_MAUVE, {});
 				DrawString(ir.left, ir.right, CenterBounds(ir.top, ir.bottom, GetCharacterHeight(FS_NORMAL)), STR_NETWORK_CONNECTING_1 + _network_join_status, TC_FROMSTRING, SA_HOR_CENTER);
 				break;
 			}
diff --git a/src/newgrf_debug_gui.cpp b/src/newgrf_debug_gui.cpp
index b063eb5a5e..6e89b32841 100644
--- a/src/newgrf_debug_gui.cpp
+++ b/src/newgrf_debug_gui.cpp
@@ -425,9 +425,9 @@ struct NewGRFInspectWindow : Window {
 
 		/* Highlight the articulated part (this is different to the whole-vehicle highlighting of DrawVehicleImage */
 		if (_current_text_dir == TD_RTL) {
-			DrawFrameRect(r.right - sel_end + skip, y, r.right - sel_start + skip, y + h, COLOUR_WHITE, FR_BORDERONLY);
+			DrawFrameRect(r.right - sel_end + skip, y, r.right - sel_start + skip, y + h, COLOUR_WHITE, FrameFlag::BorderOnly);
 		} else {
-			DrawFrameRect(r.left + sel_start - skip, y, r.left + sel_end - skip, y + h, COLOUR_WHITE, FR_BORDERONLY);
+			DrawFrameRect(r.left + sel_start - skip, y, r.left + sel_end - skip, y + h, COLOUR_WHITE, FrameFlag::BorderOnly);
 		}
 	}
 
diff --git a/src/newgrf_gui.cpp b/src/newgrf_gui.cpp
index f72cae6c37..517849e4fd 100644
--- a/src/newgrf_gui.cpp
+++ b/src/newgrf_gui.cpp
@@ -2237,10 +2237,10 @@ struct ScanProgressWindow : public Window {
 		switch (widget) {
 			case WID_SP_PROGRESS_BAR: {
 				/* Draw the % complete with a bar and a text */
-				DrawFrameRect(r, COLOUR_GREY, FR_BORDERONLY | FR_LOWERED);
+				DrawFrameRect(r, COLOUR_GREY, {FrameFlag::BorderOnly, FrameFlag::Lowered});
 				Rect ir = r.Shrink(WidgetDimensions::scaled.bevel);
 				uint percent = scanned * 100 / std::max(1U, _settings_client.gui.last_newgrf_count);
-				DrawFrameRect(ir.WithWidth(ir.Width() * percent / 100, _current_text_dir == TD_RTL), COLOUR_MAUVE, FR_NONE);
+				DrawFrameRect(ir.WithWidth(ir.Width() * percent / 100, _current_text_dir == TD_RTL), COLOUR_MAUVE, {});
 				SetDParam(0, percent);
 				DrawString(ir.left, ir.right, CenterBounds(ir.top, ir.bottom, GetCharacterHeight(FS_NORMAL)), STR_GENERATION_PROGRESS, TC_FROMSTRING, SA_HOR_CENTER);
 				break;
diff --git a/src/roadveh_gui.cpp b/src/roadveh_gui.cpp
index d623d76668..f3deefbede 100644
--- a/src/roadveh_gui.cpp
+++ b/src/roadveh_gui.cpp
@@ -163,6 +163,6 @@ void DrawRoadVehImage(const Vehicle *v, const Rect &r, VehicleID selection, Engi
 	if (v->index == selection) {
 		int height = ScaleSpriteTrad(12);
 		Rect hr = {(rtl ? px : 0), 0, (rtl ? max_width : px) - 1, height - 1};
-		DrawFrameRect(hr.Translate(r.left, CenterBounds(r.top, r.bottom, height)).Expand(WidgetDimensions::scaled.bevel), COLOUR_WHITE, FR_BORDERONLY);
+		DrawFrameRect(hr.Translate(r.left, CenterBounds(r.top, r.bottom, height)).Expand(WidgetDimensions::scaled.bevel), COLOUR_WHITE, FrameFlag::BorderOnly);
 	}
 }
diff --git a/src/settings_gui.cpp b/src/settings_gui.cpp
index 8e2cb27847..509d87c25f 100644
--- a/src/settings_gui.cpp
+++ b/src/settings_gui.cpp
@@ -2931,8 +2931,8 @@ void DrawArrowButtons(int x, int y, Colours button_colour, uint8_t state, bool c
 	Rect lr = {x,                  y, x + (int)dim.width     - 1, y + (int)dim.height - 1};
 	Rect rr = {x + (int)dim.width, y, x + (int)dim.width * 2 - 1, y + (int)dim.height - 1};
 
-	DrawFrameRect(lr, button_colour, (state == 1) ? FR_LOWERED : FR_NONE);
-	DrawFrameRect(rr, button_colour, (state == 2) ? FR_LOWERED : FR_NONE);
+	DrawFrameRect(lr, button_colour, (state == 1) ? FrameFlag::Lowered : FrameFlags{});
+	DrawFrameRect(rr, button_colour, (state == 2) ? FrameFlag::Lowered : FrameFlags{});
 	DrawSpriteIgnorePadding(SPR_ARROW_LEFT,  PAL_NONE, lr, SA_CENTER);
 	DrawSpriteIgnorePadding(SPR_ARROW_RIGHT, PAL_NONE, rr, SA_CENTER);
 
@@ -2960,7 +2960,7 @@ void DrawDropDownButton(int x, int y, Colours button_colour, bool state, bool cl
 
 	Rect r = {x, y, x + SETTING_BUTTON_WIDTH - 1, y + SETTING_BUTTON_HEIGHT - 1};
 
-	DrawFrameRect(r, button_colour, state ? FR_LOWERED : FR_NONE);
+	DrawFrameRect(r, button_colour, state ? FrameFlag::Lowered : FrameFlags{});
 	DrawSpriteIgnorePadding(SPR_ARROW_DOWN, PAL_NONE, r, SA_CENTER);
 
 	if (!clickable) {
@@ -2980,7 +2980,7 @@ void DrawBoolButton(int x, int y, bool state, bool clickable)
 	static const Colours _bool_ctabs[2][2] = {{COLOUR_CREAM, COLOUR_RED}, {COLOUR_DARK_GREEN, COLOUR_GREEN}};
 
 	Rect r = {x, y, x + SETTING_BUTTON_WIDTH - 1, y + SETTING_BUTTON_HEIGHT - 1};
-	DrawFrameRect(r, _bool_ctabs[state][clickable], state ? FR_LOWERED : FR_NONE);
+	DrawFrameRect(r, _bool_ctabs[state][clickable], state ? FrameFlag::Lowered : FrameFlags{});
 }
 
 struct CustomCurrencyWindow : Window {
diff --git a/src/ship_gui.cpp b/src/ship_gui.cpp
index 2ea017e7bc..4580cd6746 100644
--- a/src/ship_gui.cpp
+++ b/src/ship_gui.cpp
@@ -50,7 +50,7 @@ void DrawShipImage(const Vehicle *v, const Rect &r, VehicleID selection, EngineI
 		x += x_offs;
 		y += UnScaleGUI(rect.top);
 		Rect hr = {x, y, x + width - 1, y + UnScaleGUI(rect.Height()) - 1};
-		DrawFrameRect(hr.Expand(WidgetDimensions::scaled.bevel), COLOUR_WHITE, FR_BORDERONLY);
+		DrawFrameRect(hr.Expand(WidgetDimensions::scaled.bevel), COLOUR_WHITE, FrameFlag::BorderOnly);
 	}
 }
 
diff --git a/src/slider.cpp b/src/slider.cpp
index 30e0591e83..69194c402c 100644
--- a/src/slider.cpp
+++ b/src/slider.cpp
@@ -75,7 +75,7 @@ void DrawSliderWidget(Rect r, int min_value, int max_value, int nmarks, int valu
 	value -= min_value;
 	if (_current_text_dir == TD_RTL) value = max_value - value;
 	x = r.left + (value * (r.right - r.left - sw) / max_value);
-	DrawFrameRect(x, r.top, x + sw, r.bottom, COLOUR_GREY, FR_NONE);
+	DrawFrameRect(x, r.top, x + sw, r.bottom, COLOUR_GREY, {});
 }
 
 /**
diff --git a/src/story_gui.cpp b/src/story_gui.cpp
index 89761aabcb..f14bb4819c 100644
--- a/src/story_gui.cpp
+++ b/src/story_gui.cpp
@@ -734,7 +734,7 @@ public:
 				case SPET_BUTTON_TILE:
 				case SPET_BUTTON_VEHICLE: {
 					const int tmargin = WidgetDimensions::scaled.bevel.top + WidgetDimensions::scaled.frametext.top;
-					const FrameFlags frame = this->active_button_id == ce.pe->index ? FR_LOWERED : FR_NONE;
+					const FrameFlags frame = this->active_button_id == ce.pe->index ? FrameFlag::Lowered : FrameFlags{};
 					const Colours bgcolour = StoryPageButtonData{ ce.pe->referenced_id }.GetColour();
 
 					DrawFrameRect(ce.bounds.left, ce.bounds.top - scrollpos, ce.bounds.right, ce.bounds.bottom - scrollpos - 1, bgcolour, frame);
diff --git a/src/train_gui.cpp b/src/train_gui.cpp
index 38c8bb99e6..3c8734f131 100644
--- a/src/train_gui.cpp
+++ b/src/train_gui.cpp
@@ -167,7 +167,7 @@ void DrawTrainImage(const Train *v, const Rect &r, VehicleID selection, EngineIm
 		 * the next engine after the highlight could overlap it. */
 		int height = ScaleSpriteTrad(12);
 		Rect hr = {highlight_l, 0, highlight_r, height - 1};
-		DrawFrameRect(hr.Translate(r.left, CenterBounds(r.top, r.bottom, height)).Expand(WidgetDimensions::scaled.bevel), COLOUR_WHITE, FR_BORDERONLY);
+		DrawFrameRect(hr.Translate(r.left, CenterBounds(r.top, r.bottom, height)).Expand(WidgetDimensions::scaled.bevel), COLOUR_WHITE, FrameFlag::BorderOnly);
 	}
 }
 
diff --git a/src/transparency_gui.cpp b/src/transparency_gui.cpp
index 31cd44812e..4afa8330ae 100644
--- a/src/transparency_gui.cpp
+++ b/src/transparency_gui.cpp
@@ -63,7 +63,7 @@ public:
 
 					const Rect wr = this->GetWidget<NWidgetBase>(i)->GetCurrentRect().Shrink(WidgetDimensions::scaled.fullbevel);
 					DrawFrameRect(wr.left, fr.top, wr.right, fr.bottom, COLOUR_PALE_GREEN,
-							HasBit(_invisibility_opt, i - WID_TT_BEGIN) ? FR_LOWERED : FR_NONE);
+							HasBit(_invisibility_opt, i - WID_TT_BEGIN) ? FrameFlag::Lowered : FrameFlags{});
 				}
 				break;
 			}
diff --git a/src/vehicle_gui.cpp b/src/vehicle_gui.cpp
index d71d3e2414..bd2c026934 100644
--- a/src/vehicle_gui.cpp
+++ b/src/vehicle_gui.cpp
@@ -1104,7 +1104,7 @@ struct RefitWindow : public Window {
 
 								if (left != right) {
 									Rect hr = {left, highlight_top, right, highlight_bottom};
-									DrawFrameRect(hr.Expand(WidgetDimensions::scaled.bevel), COLOUR_WHITE, FR_BORDERONLY);
+									DrawFrameRect(hr.Expand(WidgetDimensions::scaled.bevel), COLOUR_WHITE, FrameFlag::BorderOnly);
 								}
 
 								left = INT32_MIN;
diff --git a/src/viewport.cpp b/src/viewport.cpp
index c888b37491..246e50fe8f 100644
--- a/src/viewport.cpp
+++ b/src/viewport.cpp
@@ -1772,10 +1772,10 @@ static void ViewportDrawStrings(ZoomLevel zoom, const StringSpriteToDrawVector *
 
 		TextColour colour = TC_WHITE;
 		if (ss.flags.Test(ViewportStringFlag::ColourRect)) {
-			if (ss.colour != INVALID_COLOUR) DrawFrameRect(x, y, x + w - 1, y + h - 1, ss.colour, FR_NONE);
+			if (ss.colour != INVALID_COLOUR) DrawFrameRect(x, y, x + w - 1, y + h - 1, ss.colour, {});
 			colour = TC_BLACK;
 		} else if (ss.flags.Test(ViewportStringFlag::TransparentRect)) {
-			DrawFrameRect(x, y, x + w - 1, y + h - 1, ss.colour, FR_TRANSPARENT);
+			DrawFrameRect(x, y, x + w - 1, y + h - 1, ss.colour, FrameFlag::Transparent);
 		}
 
 		if (ss.flags.Test(ViewportStringFlag::TextColour)) {
diff --git a/src/widget.cpp b/src/widget.cpp
index bf106a5cef..d9a08617f2 100644
--- a/src/widget.cpp
+++ b/src/widget.cpp
@@ -282,7 +282,7 @@ WidgetID GetWidgetFromPos(const Window *w, int x, int y)
  */
 void DrawFrameRect(int left, int top, int right, int bottom, Colours colour, FrameFlags flags)
 {
-	if (flags & FR_TRANSPARENT) {
+	if (flags.Test(FrameFlag::Transparent)) {
 		GfxFillRect(left, top, right, bottom, PALETTE_TO_TRANSPARENT, FILLRECT_RECOLOUR);
 	} else {
 		assert(colour < COLOUR_END);
@@ -296,12 +296,12 @@ void DrawFrameRect(int left, int top, int right, int bottom, Colours colour, Fra
 		Rect outer = {left, top, right, bottom};                   // Outside rectangle
 		Rect inner = outer.Shrink(WidgetDimensions::scaled.bevel); // Inside rectangle
 
-		if (flags & FR_LOWERED) {
+		if (flags.Test(FrameFlag::Lowered)) {
 			GfxFillRect(outer.left,      outer.top,        inner.left - 1,  outer.bottom, dark);   // Left
 			GfxFillRect(inner.left,      outer.top,        outer.right,     inner.top - 1, dark);  // Top
 			GfxFillRect(inner.right + 1, inner.top,        outer.right,     inner.bottom,  light); // Right
 			GfxFillRect(inner.left,      inner.bottom + 1, outer.right,     outer.bottom, light);  // Bottom
-			interior = (flags & FR_DARKENED ? medium_dark : medium_light);
+			interior = (flags.Test(FrameFlag::Darkened) ? medium_dark : medium_light);
 		} else {
 			GfxFillRect(outer.left,      outer.top,        inner.left - 1, inner.bottom,  light); // Left
 			GfxFillRect(inner.left,      outer.top,        inner.right,    inner.top - 1, light); // Top
@@ -309,7 +309,7 @@ void DrawFrameRect(int left, int top, int right, int bottom, Colours colour, Fra
 			GfxFillRect(outer.left,      inner.bottom + 1, outer.right,    outer.bottom, dark);   // Bottom
 			interior = medium_dark;
 		}
-		if (!(flags & FR_BORDERONLY)) {
+		if (!flags.Test(FrameFlag::BorderOnly)) {
 			GfxFillRect(inner.left,  inner.top, inner.right, inner.bottom, interior); // Inner
 		}
 	}
@@ -338,7 +338,7 @@ void DrawSpriteIgnorePadding(SpriteID img, PaletteID pal, const Rect &r, StringA
 static inline void DrawImageButtons(const Rect &r, WidgetType type, Colours colour, bool clicked, SpriteID img, StringAlignment align)
 {
 	assert(img != 0);
-	DrawFrameRect(r.left, r.top, r.right, r.bottom, colour, (clicked) ? FR_LOWERED : FR_NONE);
+	DrawFrameRect(r.left, r.top, r.right, r.bottom, colour, (clicked) ? FrameFlag::Lowered : FrameFlags{});
 
 	if ((type & WWT_MASK) == WWT_IMGBTN_2 && clicked) img++; // Show different image when clicked for #WWT_IMGBTN_2.
 	DrawSpriteIgnorePadding(img, PAL_NONE, r, align);
@@ -389,7 +389,7 @@ static inline void DrawText(const Rect &r, TextColour colour, StringID str, Stri
  */
 static inline void DrawInset(const Rect &r, Colours colour, TextColour text_colour, StringID str, StringAlignment align, FontSize fs)
 {
-	DrawFrameRect(r.left, r.top, r.right, r.bottom, colour, FR_LOWERED | FR_DARKENED);
+	DrawFrameRect(r.left, r.top, r.right, r.bottom, colour, {FrameFlag::Lowered, FrameFlag::Darkened});
 	if (str != STR_NULL) DrawString(r.Shrink(WidgetDimensions::scaled.inset), str, text_colour, align, false, fs);
 }
 
@@ -405,7 +405,7 @@ static inline void DrawInset(const Rect &r, Colours colour, TextColour text_colo
  */
 static inline void DrawMatrix(const Rect &r, Colours colour, bool clicked, uint32_t num_columns, uint32_t num_rows, uint resize_x, uint resize_y)
 {
-	DrawFrameRect(r.left, r.top, r.right, r.bottom, colour, (clicked) ? FR_LOWERED : FR_NONE);
+	DrawFrameRect(r.left, r.top, r.right, r.bottom, colour, (clicked) ? FrameFlag::Lowered : FrameFlags{});
 
 	int column_width; // Width of a single column in the matrix.
 	if (num_columns == 0) {
@@ -489,7 +489,7 @@ static inline void DrawVerticalScrollbar(const Rect &r, Colours colour, bool up_
 	GfxFillRect(right,      r.top + height, right + br - 1, r.bottom - height, c2);
 
 	Point pt = HandleScrollbarHittest(scrollbar, r.top, r.bottom, false);
-	DrawFrameRect(r.left, pt.x, r.right, pt.y, colour, bar_dragged ? FR_LOWERED : FR_NONE);
+	DrawFrameRect(r.left, pt.x, r.right, pt.y, colour, bar_dragged ? FrameFlag::Lowered : FrameFlags{});
 }
 
 /**
@@ -529,7 +529,7 @@ static inline void DrawHorizontalScrollbar(const Rect &r, Colours colour, bool l
 
 	/* draw actual scrollbar */
 	Point pt = HandleScrollbarHittest(scrollbar, r.left, r.right, true);
-	DrawFrameRect(pt.x, r.top, pt.y, r.bottom, colour, bar_dragged ? FR_LOWERED : FR_NONE);
+	DrawFrameRect(pt.x, r.top, pt.y, r.bottom, colour, bar_dragged ? FrameFlag::Lowered : FrameFlags{});
 }
 
 /**
@@ -643,7 +643,7 @@ static inline void DrawDebugBox(const Rect &r, Colours colour, bool clicked)
 static inline void DrawResizeBox(const Rect &r, Colours colour, bool at_left, bool clicked, bool bevel)
 {
 	if (bevel) {
-		DrawFrameRect(r.left, r.top, r.right, r.bottom, colour, (clicked) ? FR_LOWERED : FR_NONE);
+		DrawFrameRect(r.left, r.top, r.right, r.bottom, colour, (clicked) ? FrameFlag::Lowered : FrameFlags{});
 	} else if (clicked) {
 		GfxFillRect(r.Shrink(WidgetDimensions::scaled.bevel), GetColourGradient(colour, SHADE_LIGHTER));
 	}
@@ -657,7 +657,7 @@ static inline void DrawResizeBox(const Rect &r, Colours colour, bool at_left, bo
  */
 static inline void DrawCloseBox(const Rect &r, Colours colour)
 {
-	if (colour != COLOUR_WHITE) DrawFrameRect(r.left, r.top, r.right, r.bottom, colour, FR_NONE);
+	if (colour != COLOUR_WHITE) DrawFrameRect(r.left, r.top, r.right, r.bottom, colour, {});
 	Point offset;
 	Dimension d = GetSpriteSize(SPR_CLOSEBOX, &offset);
 	d.width  -= offset.x;
@@ -680,9 +680,9 @@ void DrawCaption(const Rect &r, Colours colour, Owner owner, TextColour text_col
 {
 	bool company_owned = owner < MAX_COMPANIES;
 
-	DrawFrameRect(r, colour, FR_BORDERONLY);
+	DrawFrameRect(r, colour, FrameFlag::BorderOnly);
 	Rect ir = r.Shrink(WidgetDimensions::scaled.bevel);
-	DrawFrameRect(ir, colour, company_owned ? FR_LOWERED | FR_DARKENED | FR_BORDERONLY : FR_LOWERED | FR_DARKENED);
+	DrawFrameRect(ir, colour, company_owned ? FrameFlags{FrameFlag::Lowered, FrameFlag::Darkened, FrameFlag::BorderOnly} : FrameFlags{FrameFlag::Lowered, FrameFlag::Darkened});
 
 	if (company_owned) {
 		GfxFillRect(ir.Shrink(WidgetDimensions::scaled.bevel), GetColourGradient(_company_colours[owner], SHADE_NORMAL));
@@ -711,13 +711,13 @@ static inline void DrawButtonDropdown(const Rect &r, Colours colour, bool clicke
 	int dd_width  = NWidgetLeaf::dropdown_dimension.width;
 
 	if (_current_text_dir == TD_LTR) {
-		DrawFrameRect(r.left, r.top, r.right - dd_width, r.bottom, colour, clicked_button ? FR_LOWERED : FR_NONE);
+		DrawFrameRect(r.left, r.top, r.right - dd_width, r.bottom, colour, clicked_button ? FrameFlag::Lowered : FrameFlags{});
 		DrawImageButtons(r.WithWidth(dd_width, true), WWT_DROPDOWN, colour, clicked_dropdown, SPR_ARROW_DOWN, SA_CENTER);
 		if (str != STR_NULL) {
 			DrawString(r.left + WidgetDimensions::scaled.dropdowntext.left, r.right - dd_width - WidgetDimensions::scaled.dropdowntext.right, CenterBounds(r.top, r.bottom, GetCharacterHeight(FS_NORMAL)), str, TC_BLACK, align);
 		}
 	} else {
-		DrawFrameRect(r.left + dd_width, r.top, r.right, r.bottom, colour, clicked_button ? FR_LOWERED : FR_NONE);
+		DrawFrameRect(r.left + dd_width, r.top, r.right, r.bottom, colour, clicked_button ? FrameFlag::Lowered : FrameFlags{});
 		DrawImageButtons(r.WithWidth(dd_width, false), WWT_DROPDOWN, colour, clicked_dropdown, SPR_ARROW_DOWN, SA_CENTER);
 		if (str != STR_NULL) {
 			DrawString(r.left + dd_width + WidgetDimensions::scaled.dropdowntext.left, r.right - WidgetDimensions::scaled.dropdowntext.right, CenterBounds(r.top, r.bottom, GetCharacterHeight(FS_NORMAL)), str, TC_BLACK, align);
@@ -733,7 +733,7 @@ void Window::DrawWidgets() const
 	this->nested_root->Draw(this);
 
 	if (this->flags.Test(WindowFlag::WhiteBorder)) {
-		DrawFrameRect(0, 0, this->width - 1, this->height - 1, COLOUR_WHITE, FR_BORDERONLY);
+		DrawFrameRect(0, 0, this->width - 1, this->height - 1, COLOUR_WHITE, FrameFlag::BorderOnly);
 	}
 
 	if (this->flags.Test(WindowFlag::Highlighted)) {
@@ -2341,7 +2341,7 @@ void NWidgetBackground::Draw(const Window *w)
 
 	switch (this->type) {
 		case WWT_PANEL:
-			DrawFrameRect(r.left, r.top, r.right, r.bottom, this->colour, this->IsLowered() ? FR_LOWERED : FR_NONE);
+			DrawFrameRect(r.left, r.top, r.right, r.bottom, this->colour, this->IsLowered() ? FrameFlag::Lowered : FrameFlags{});
 			break;
 
 		case WWT_FRAME:
@@ -3003,7 +3003,7 @@ void NWidgetLeaf::Draw(const Window *w)
 			break;
 
 		case WWT_PUSHBTN:
-			DrawFrameRect(r.left, r.top, r.right, r.bottom, this->colour, (clicked) ? FR_LOWERED : FR_NONE);
+			DrawFrameRect(r.left, r.top, r.right, r.bottom, this->colour, (clicked) ? FrameFlag::Lowered : FrameFlags{});
 			break;
 
 		case WWT_IMGBTN:
@@ -3016,7 +3016,7 @@ void NWidgetLeaf::Draw(const Window *w)
 		case WWT_PUSHTXTBTN:
 		case WWT_TEXTBTN_2:
 			if (this->index >= 0) w->SetStringParameters(this->index);
-			DrawFrameRect(r.left, r.top, r.right, r.bottom, this->colour, (clicked) ? FR_LOWERED : FR_NONE);
+			DrawFrameRect(r.left, r.top, r.right, r.bottom, this->colour, (clicked) ? FrameFlag::Lowered : FrameFlags{});
 			DrawLabel(r, this->type, clicked, this->text_colour, this->GetString(), this->align, this->text_size);
 			break;
 
diff --git a/src/window_gui.h b/src/window_gui.h
index d49a9b7d39..11722365a6 100644
--- a/src/window_gui.h
+++ b/src/window_gui.h
@@ -21,15 +21,13 @@
 /**
  * Flags to describe the look of the frame
  */
-enum FrameFlags : uint8_t {
-	FR_NONE         =  0,
-	FR_TRANSPARENT  =  1 << 0,  ///< Makes the background transparent if set
-	FR_BORDERONLY   =  1 << 4,  ///< Draw border only, no background
-	FR_LOWERED      =  1 << 5,  ///< If set the frame is lowered and the background colour brighter (ie. buttons when pressed)
-	FR_DARKENED     =  1 << 6,  ///< If set the background is darker, allows for lowered frames with normal background colour when used with FR_LOWERED (ie. dropdown boxes)
+enum class FrameFlag : uint8_t {
+	Transparent, ///< Makes the background transparent if set
+	BorderOnly, ///< Draw border only, no background
+	Lowered, ///< If set the frame is lowered and the background colour brighter (ie. buttons when pressed)
+	Darkened, ///< If set the background is darker, allows for lowered frames with normal background colour when used with FrameFlag::Lowered (ie. dropdown boxes)
 };
-
-DECLARE_ENUM_AS_BIT_SET(FrameFlags)
+using FrameFlags = EnumBitSet<FrameFlag, uint8_t>;
 
 class WidgetDimensions {
 public: