diff --git a/src/misc/dbg_helpers.cpp b/src/misc/dbg_helpers.cpp
index 63b348e73c..7e2d4314c4 100644
--- a/src/misc/dbg_helpers.cpp
+++ b/src/misc/dbg_helpers.cpp
@@ -106,31 +106,17 @@ void DumpTarget::WriteIndent()
 	}
 }
 
-/** Write 'name = value' with indent and new-line. */
-void DumpTarget::WriteValue(const std::string &name, int value)
-{
-	WriteIndent();
-	m_out += name + " = " + std::to_string(value) + "\n";
-}
-
-/** Write 'name = value' with indent and new-line. */
-void DumpTarget::WriteValue(const std::string &name, const std::string &value_str)
-{
-	WriteIndent();
-	m_out += name + " = " + value_str + "\n";
-}
-
 /** Write name & TileIndex to the output. */
-void DumpTarget::WriteTile(const std::string &name, TileIndex tile)
+void DumpTarget::WriteTile(std::string_view name, TileIndex tile)
 {
 	WriteIndent();
-	m_out += name + " = " + TileStr(tile) + "\n";
+	format_append(m_out, "{} = {}\n", name, TileStr(tile));
 }
 
 /**
  * Open new structure (one level deeper than the current one) 'name = {\<LF\>'.
  */
-void DumpTarget::BeginStruct(size_t type_id, const std::string &name, const void *ptr)
+void DumpTarget::BeginStruct(size_t type_id, std::string_view name, const void *ptr)
 {
 	/* make composite name */
 	std::string cur_name = GetCurrentStructName();
@@ -147,7 +133,7 @@ void DumpTarget::BeginStruct(size_t type_id, const std::string &name, const void
 	m_known_names.insert(KNOWN_NAMES::value_type(KnownStructKey(type_id, ptr), cur_name));
 
 	WriteIndent();
-	m_out += name + " = {\n";
+	format_append(m_out, "{} = {{\n", name);
 	m_indent++;
 }
 
diff --git a/src/misc/dbg_helpers.h b/src/misc/dbg_helpers.h
index e67e929edb..f34dd85bba 100644
--- a/src/misc/dbg_helpers.h
+++ b/src/misc/dbg_helpers.h
@@ -16,6 +16,7 @@
 #include "../signal_type.h"
 #include "../tile_type.h"
 #include "../track_type.h"
+#include "../core/format.hpp"
 
 /** Helper template class that provides C array length and item type */
 template <typename T> struct ArrayT;
@@ -156,21 +157,26 @@ struct DumpTarget {
 
 	void WriteIndent();
 
-	void WriteValue(const std::string &name, int value);
-	void WriteValue(const std::string &name, const std::string &value_str);
-	void WriteTile(const std::string &name, TileIndex t);
+	/** Write 'name = value' with indent and new-line. */
+	void WriteValue(std::string_view name, const auto &value)
+	{
+		WriteIndent();
+		format_append(m_out, "{} = {}\n", name, value);
+	}
+
+	void WriteTile(std::string_view name, TileIndex t);
 
 	/** Dump given enum value (as a number and as named value) */
-	template <typename E> void WriteEnumT(const std::string &name, E e)
+	template <typename E> void WriteEnumT(std::string_view name, E e)
 	{
 		WriteValue(name, ValueStr(e));
 	}
 
-	void BeginStruct(size_t type_id, const std::string &name, const void *ptr);
+	void BeginStruct(size_t type_id, std::string_view name, const void *ptr);
 	void EndStruct();
 
 	/** Dump nested object (or only its name if this instance is already known). */
-	template <typename S> void WriteStructT(const std::string &name, const S *s)
+	template <typename S> void WriteStructT(std::string_view name, const S *s)
 	{
 		static size_t type_id = ++LastTypeId();
 
@@ -193,7 +199,7 @@ struct DumpTarget {
 	}
 
 	/** Dump nested object (or only its name if this instance is already known). */
-	template <typename S> void WriteStructT(const std::string &name, const std::deque<S> *s)
+	template <typename S> void WriteStructT(std::string_view name, const std::deque<S> *s)
 	{
 		static size_t type_id = ++LastTypeId();
 
@@ -211,7 +217,7 @@ struct DumpTarget {
 			/* Still unknown, dump it */
 			BeginStruct(type_id, name, s);
 			size_t num_items = s->size();
-			this->WriteValue("num_items", std::to_string(num_items));
+			this->WriteValue("num_items", num_items);
 			for (size_t i = 0; i < num_items; i++) {
 				const auto &item = (*s)[i];
 				this->WriteStructT(fmt::format("item[{}]", i), &item);
diff --git a/src/music/midifile.cpp b/src/music/midifile.cpp
index e581bc342c..9985c96e85 100644
--- a/src/music/midifile.cpp
+++ b/src/music/midifile.cpp
@@ -1065,7 +1065,7 @@ std::string MidiFile::GetSMFFile(const MusicSongInfo &song)
 	AppendPathSeparator(tempdirname);
 	FioCreateDirectory(tempdirname);
 
-	std::string output_filename = tempdirname + std::to_string(song.cat_index) + ".mid";
+	std::string output_filename = fmt::format("{}{}.mid", tempdirname, song.cat_index);
 
 	if (FileExists(output_filename)) {
 		/* If the file already exists, assume it's the correct decoded data */
diff --git a/src/network/core/address.cpp b/src/network/core/address.cpp
index ff667aab7f..ebb27f58ca 100644
--- a/src/network/core/address.cpp
+++ b/src/network/core/address.cpp
@@ -209,7 +209,7 @@ SOCKET NetworkAddress::Resolve(int family, int socktype, int flags, SocketList *
 	hints.ai_socktype = socktype;
 
 	/* The port needs to be a string. Six is enough to contain all characters + '\0'. */
-	std::string port_name = std::to_string(this->GetPort());
+	std::string port_name = fmt::format("{}", this->GetPort());
 
 	bool reset_hostname = false;
 	/* Setting both hostname to nullptr and port to 0 is not allowed.
diff --git a/src/network/core/tcp_connect.cpp b/src/network/core/tcp_connect.cpp
index 0862bdc6a6..44a4f550d1 100644
--- a/src/network/core/tcp_connect.cpp
+++ b/src/network/core/tcp_connect.cpp
@@ -228,7 +228,7 @@ void TCPConnecter::Resolve()
 	hints.ai_flags = AI_ADDRCONFIG;
 	hints.ai_socktype = SOCK_STREAM;
 
-	std::string port_name = std::to_string(address.GetPort());
+	std::string port_name = fmt::format("{}", address.GetPort());
 
 	static bool getaddrinfo_timeout_error_shown = false;
 	auto start = std::chrono::steady_clock::now();
diff --git a/src/network/network_content.cpp b/src/network/network_content.cpp
index e67fecfaec..cdbe3de668 100644
--- a/src/network/network_content.cpp
+++ b/src/network/network_content.cpp
@@ -323,7 +323,7 @@ void ClientNetworkContentSocketHandler::DownloadSelectedContentHTTP(const Conten
 {
 	std::string content_request;
 	for (const ContentID &id : content) {
-		content_request += std::to_string(id) + "\n";
+		format_append(content_request, "{}\n", id);
 	}
 
 	this->http_response_index = -1;
diff --git a/src/network/network_server.cpp b/src/network/network_server.cpp
index 6e9459c646..862057107e 100644
--- a/src/network/network_server.cpp
+++ b/src/network/network_server.cpp
@@ -1627,7 +1627,7 @@ bool NetworkMakeClientNameUnique(std::string &name)
 
 		if (!is_name_unique) {
 			/* Try a new name (<name> #1, <name> #2, and so on) */
-			name = original_name + " #" + std::to_string(number);
+			name = fmt::format("{} #{}", original_name, number);
 
 			/* The constructed client name is larger than the limit,
 			 * so... bail out as no valid name can be created. */
diff --git a/src/newgrf_config.cpp b/src/newgrf_config.cpp
index 5b7db9b30d..eb4862c7a0 100644
--- a/src/newgrf_config.cpp
+++ b/src/newgrf_config.cpp
@@ -643,7 +643,7 @@ std::string GRFBuildParamList(const GRFConfig &c)
 	std::string result;
 	for (const uint32_t &value : c.param) {
 		if (!result.empty()) result += ' ';
-		result += std::to_string(value);
+		format_append(result, "{}", value);
 	}
 	return result;
 }
diff --git a/src/pathfinder/water_regions.cpp b/src/pathfinder/water_regions.cpp
index 10597c0cef..7c327cd6a4 100644
--- a/src/pathfinder/water_regions.cpp
+++ b/src/pathfinder/water_regions.cpp
@@ -196,7 +196,7 @@ public:
 	{
 		Debug(map, 9, "Water region {},{} labels and edge traversability = ...", GetWaterRegionX(this->tile_area.tile), GetWaterRegionY(this->tile_area.tile));
 
-		const size_t max_element_width = std::to_string(this->NumberOfPatches()).size();
+		const size_t max_element_width = fmt::format("{}", this->NumberOfPatches()).size();
 
 		std::string traversability = fmt::format("{:0{}b}", this->GetEdgeTraversabilityBits(DIAGDIR_NW), WATER_REGION_EDGE_LENGTH);
 		Debug(map, 9, "    {:{}}", fmt::join(traversability, " "), max_element_width);
@@ -206,8 +206,11 @@ public:
 			std::string line{};
 			for (int x = 0; x < WATER_REGION_EDGE_LENGTH; ++x) {
 				const auto label = this->GetLabel(TileAddXY(this->tile_area.tile, x, y));
-				const std::string label_str = label == INVALID_WATER_REGION_PATCH ? "." : std::to_string(label);
-				line = fmt::format("{:{}}", label_str, max_element_width) + " " + line;
+				if (label == INVALID_WATER_REGION_PATCH) {
+					line = fmt::format("{:{}} {}", ".", max_element_width, line);
+				} else {
+					line = fmt::format("{:{}} {}", label, max_element_width, line);
+				}
 			}
 			Debug(map, 9, "{} | {}| {}", GB(this->GetEdgeTraversabilityBits(DIAGDIR_SW), y, 1), line, GB(this->GetEdgeTraversabilityBits(DIAGDIR_NE), y, 1));
 		}
diff --git a/src/safeguards.h b/src/safeguards.h
index d00c7c0c71..70a272cbf9 100644
--- a/src/safeguards.h
+++ b/src/safeguards.h
@@ -67,6 +67,9 @@
 #define fputs     SAFEGUARD_DO_NOT_USE_THIS_METHOD
 #define putchar   SAFEGUARD_DO_NOT_USE_THIS_METHOD
 
+/* Use fmt::format instead */
+#define to_string SAFEGUARD_DO_NOT_USE_THIS_METHOD
+
 /* Use our own templated implementation instead of a macro or function with only one type. */
 #ifdef min
 #undef min
diff --git a/src/settings.cpp b/src/settings.cpp
index d54048112d..7a86bfa46a 100644
--- a/src/settings.cpp
+++ b/src/settings.cpp
@@ -324,7 +324,7 @@ std::string ListSettingDesc::FormatValue(const void *object) const
 			default: NOT_REACHED();
 		}
 		if (i != 0) result += ',';
-		result += std::to_string(v);
+		format_append(result, "{}", v);
 	}
 	return result;
 }
@@ -332,7 +332,7 @@ std::string ListSettingDesc::FormatValue(const void *object) const
 std::string OneOfManySettingDesc::FormatSingleValue(uint id) const
 {
 	if (id >= this->many.size()) {
-		return std::to_string(id);
+		return fmt::format("{}", id);
 	}
 	return this->many[id];
 }
@@ -735,7 +735,7 @@ std::string IntSettingDesc::FormatValue(const void *object) const
 	} else {
 		i = (uint32_t)this->Read(object);
 	}
-	return std::to_string(i);
+	return fmt::format("{}", i);
 }
 
 std::string BoolSettingDesc::FormatValue(const void *object) const
@@ -1218,7 +1218,7 @@ static void SaveVersionInConfig(IniFile &ini)
 	IniGroup &group = ini.GetOrCreateGroup("version");
 	group.GetOrCreateItem("version_string").SetValue(_openttd_revision);
 	group.GetOrCreateItem("version_number").SetValue(fmt::format("{:08X}", _openttd_newgrf_version));
-	group.GetOrCreateItem("ini_version").SetValue(std::to_string(INIFILE_VERSION));
+	group.GetOrCreateItem("ini_version").SetValue(fmt::format("{}", INIFILE_VERSION));
 }
 
 /**
diff --git a/src/survey.cpp b/src/survey.cpp
index 838a702fb1..19c829d90a 100644
--- a/src/survey.cpp
+++ b/src/survey.cpp
@@ -311,7 +311,7 @@ void SurveyFont(nlohmann::json &survey)
 void SurveyCompanies(nlohmann::json &survey)
 {
 	for (const Company *c : Company::Iterate()) {
-		auto &company = survey[std::to_string(c->index.base())];
+		auto &company = survey[fmt::format("{}", c->index.base())];
 		if (c->ai_info == nullptr) {
 			company["type"] = "human";
 		} else {