diff --git a/src/viewport.cpp b/src/viewport.cpp
index 9c91b28833..98f40b2a42 100644
--- a/src/viewport.cpp
+++ b/src/viewport.cpp
@@ -1314,7 +1314,7 @@ void ViewportAddString(const DrawPixelInfo *dpi, ZoomLevel small_from, const Vie
 	int right  = left + dpi->width;
 	int bottom = top + dpi->height;
 
-	int sign_height     = ScaleByZoom(WidgetDimensions::scaled.fullbevel.top + GetCharacterHeight(FS_NORMAL) + WidgetDimensions::scaled.fullbevel.bottom, dpi->zoom);
+	int sign_height     = ScaleByZoom(WidgetDimensions::scaled.fullbevel.top + GetCharacterHeight(small ? FS_SMALL : FS_NORMAL) + WidgetDimensions::scaled.fullbevel.bottom, dpi->zoom);
 	int sign_half_width = ScaleByZoom((small ? sign->width_small : sign->width_normal) / 2, dpi->zoom);
 
 	if (bottom < sign->top ||
@@ -1338,8 +1338,7 @@ void ViewportAddString(const DrawPixelInfo *dpi, ZoomLevel small_from, const Vie
 
 static Rect ExpandRectWithViewportSignMargins(Rect r, ZoomLevel zoom)
 {
-	/* Pessimistically always use normal font, but also assume small font is never larger in either dimension */
-	const int fh = GetCharacterHeight(FS_NORMAL);
+	const int fh = std::max(GetCharacterHeight(FS_NORMAL), GetCharacterHeight(FS_SMALL));
 	const int max_tw = _viewport_sign_maxwidth / 2 + 1;
 	const int expand_y = ScaleByZoom(WidgetDimensions::scaled.fullbevel.top + fh + WidgetDimensions::scaled.fullbevel.bottom, zoom);
 	const int expand_x = ScaleByZoom(WidgetDimensions::scaled.fullbevel.left + max_tw + WidgetDimensions::scaled.fullbevel.right, zoom);
@@ -1490,12 +1489,16 @@ void ViewportSign::MarkDirty(ZoomLevel maxzoom) const
 {
 	Rect zoomlevels[ZOOM_LVL_END];
 
+	/* We don't know which size will be drawn, so mark the largest area dirty. */
+	const uint half_width = std::max(this->width_normal, this->width_small) / 2 + 1;
+	const uint height = WidgetDimensions::scaled.fullbevel.top + std::max(GetCharacterHeight(FS_NORMAL), GetCharacterHeight(FS_SMALL)) + WidgetDimensions::scaled.fullbevel.bottom + 1;
+
 	for (ZoomLevel zoom = ZOOM_LVL_BEGIN; zoom != ZOOM_LVL_END; zoom++) {
 		/* FIXME: This doesn't switch to width_small when appropriate. */
-		zoomlevels[zoom].left   = this->center - ScaleByZoom(this->width_normal / 2 + 1, zoom);
+		zoomlevels[zoom].left   = this->center - ScaleByZoom(half_width, zoom);
 		zoomlevels[zoom].top    = this->top    - ScaleByZoom(1, zoom);
-		zoomlevels[zoom].right  = this->center + ScaleByZoom(this->width_normal / 2 + 1, zoom);
-		zoomlevels[zoom].bottom = this->top    + ScaleByZoom(WidgetDimensions::scaled.fullbevel.top + GetCharacterHeight(FS_NORMAL) + WidgetDimensions::scaled.fullbevel.bottom + 1, zoom);
+		zoomlevels[zoom].right  = this->center + ScaleByZoom(half_width, zoom);
+		zoomlevels[zoom].bottom = this->top    + ScaleByZoom(height, zoom);
 	}
 
 	for (const Window *w : Window::Iterate()) {
@@ -1709,7 +1712,7 @@ static void ViewportDrawStrings(ZoomLevel zoom, const StringSpriteToDrawVector *
 		int w = GB(ss.width, 0, 15);
 		int x = UnScaleByZoom(ss.x, zoom);
 		int y = UnScaleByZoom(ss.y, zoom);
-		int h = WidgetDimensions::scaled.fullbevel.top + (small ? GetCharacterHeight(FS_SMALL) : GetCharacterHeight(FS_NORMAL)) + WidgetDimensions::scaled.fullbevel.bottom;
+		int h = WidgetDimensions::scaled.fullbevel.top + GetCharacterHeight(small ? FS_SMALL : FS_NORMAL) + WidgetDimensions::scaled.fullbevel.bottom;
 
 		if (ss.colour != INVALID_COLOUR) {
 			if (IsTransparencySet(TO_SIGNS) && ss.string_id != STR_WHITE_SIGN) {
@@ -2194,7 +2197,7 @@ static bool CheckClickOnViewportSign(const Viewport *vp, int x, int y, const Vie
 {
 	bool small = (vp->zoom >= ZOOM_LVL_OUT_4X);
 	int sign_half_width = ScaleByZoom((small ? sign->width_small : sign->width_normal) / 2, vp->zoom);
-	int sign_height = ScaleByZoom(WidgetDimensions::scaled.fullbevel.top + (small ? GetCharacterHeight(FS_SMALL) : GetCharacterHeight(FS_NORMAL)) + WidgetDimensions::scaled.fullbevel.bottom, vp->zoom);
+	int sign_height = ScaleByZoom(WidgetDimensions::scaled.fullbevel.top + GetCharacterHeight(small ? FS_SMALL : FS_NORMAL) + WidgetDimensions::scaled.fullbevel.bottom, vp->zoom);
 
 	return y >= sign->top && y < sign->top + sign_height &&
 			x >= sign->center - sign_half_width && x < sign->center + sign_half_width;
@@ -2296,7 +2299,7 @@ ViewportSignKdtreeItem ViewportSignKdtreeItem::MakeStation(StationID id)
 	item.top = st->sign.top;
 
 	/* Assume the sign can be a candidate for drawing, so measure its width */
-	_viewport_sign_maxwidth = std::max<int>(_viewport_sign_maxwidth, st->sign.width_normal);
+	_viewport_sign_maxwidth = std::max<int>({_viewport_sign_maxwidth, st->sign.width_normal, st->sign.width_small});
 
 	return item;
 }
@@ -2313,7 +2316,7 @@ ViewportSignKdtreeItem ViewportSignKdtreeItem::MakeWaypoint(StationID id)
 	item.top = st->sign.top;
 
 	/* Assume the sign can be a candidate for drawing, so measure its width */
-	_viewport_sign_maxwidth = std::max<int>(_viewport_sign_maxwidth, st->sign.width_normal);
+	_viewport_sign_maxwidth = std::max<int>({_viewport_sign_maxwidth, st->sign.width_normal, st->sign.width_small});
 
 	return item;
 }
@@ -2330,7 +2333,7 @@ ViewportSignKdtreeItem ViewportSignKdtreeItem::MakeTown(TownID id)
 	item.top = town->cache.sign.top;
 
 	/* Assume the sign can be a candidate for drawing, so measure its width */
-	_viewport_sign_maxwidth = std::max<int>(_viewport_sign_maxwidth, town->cache.sign.width_normal);
+	_viewport_sign_maxwidth = std::max<int>({_viewport_sign_maxwidth, town->cache.sign.width_normal, town->cache.sign.width_small});
 
 	return item;
 }
@@ -2347,7 +2350,7 @@ ViewportSignKdtreeItem ViewportSignKdtreeItem::MakeSign(SignID id)
 	item.top = sign->sign.top;
 
 	/* Assume the sign can be a candidate for drawing, so measure its width */
-	_viewport_sign_maxwidth = std::max<int>(_viewport_sign_maxwidth, sign->sign.width_normal);
+	_viewport_sign_maxwidth = std::max<int>({_viewport_sign_maxwidth, sign->sign.width_normal, sign->sign.width_small});
 
 	return item;
 }