diff --git a/Source/CMakeLists.txt b/Source/CMakeLists.txt
index 49d1a8477..d9bc5b8e6 100644
--- a/Source/CMakeLists.txt
+++ b/Source/CMakeLists.txt
@@ -161,6 +161,7 @@ set(libdevilutionx_SRCS
   utils/sdl_bilinear_scale.cpp
   utils/sdl_thread.cpp
   utils/str_cat.cpp
+  utils/str_case.cpp
   utils/surface_to_clx.cpp
   utils/utf8.cpp)
 
diff --git a/Source/control.cpp b/Source/control.cpp
index 3c3aa45ab..4944cdc40 100644
--- a/Source/control.cpp
+++ b/Source/control.cpp
@@ -49,6 +49,7 @@
 #include "utils/log.hpp"
 #include "utils/sdl_geometry.h"
 #include "utils/stdcompat/optional.hpp"
+#include "utils/str_case.hpp"
 #include "utils/str_cat.hpp"
 #include "utils/string_or_view.hpp"
 #include "utils/utf8.hpp"
@@ -442,11 +443,9 @@ std::string TextCmdInspect(const string_view parameter)
 		return ret;
 	}
 
-	std::string param { parameter.data() };
-	std::transform(param.begin(), param.end(), param.begin(), [](unsigned char c) { return std::tolower(c); });
+	const std::string param = AsciiStrToLower(parameter);
 	for (auto &player : Players) {
-		std::string playerName { player._pName };
-		std::transform(playerName.begin(), playerName.end(), playerName.begin(), [](unsigned char c) { return std::tolower(c); });
+		const std::string playerName = AsciiStrToLower(player._pName);
 		if (playerName.find(param) != std::string::npos) {
 			InspectPlayer = &player;
 			StrAppend(ret, _("Inspecting player: "));
diff --git a/Source/debug.cpp b/Source/debug.cpp
index 5e1eff9f2..189d82f32 100644
--- a/Source/debug.cpp
+++ b/Source/debug.cpp
@@ -32,6 +32,7 @@
 #include "utils/file_util.h"
 #include "utils/language.h"
 #include "utils/log.hpp"
+#include "utils/str_case.hpp"
 #include "utils/str_cat.hpp"
 #include "utils/str_split.hpp"
 
@@ -669,14 +670,13 @@ std::string DebugCmdSpawnUniqueMonster(const string_view parameter)
 		return "Monster name cannot be empty. Duh.";
 
 	name.pop_back(); // remove last space
-	std::transform(name.begin(), name.end(), name.begin(), [](unsigned char c) { return std::tolower(c); });
+	AsciiStrToLower(name);
 
 	int mtype = -1;
 	UniqueMonsterType uniqueIndex = UniqueMonsterType::None;
 	for (size_t i = 0; UniqueMonstersData[i].mtype != MT_INVALID; i++) {
 		auto mondata = UniqueMonstersData[i];
-		std::string monsterName(mondata.mName);
-		std::transform(monsterName.begin(), monsterName.end(), monsterName.begin(), [](unsigned char c) { return std::tolower(c); });
+		const std::string monsterName = AsciiStrToLower(mondata.mName);
 		if (monsterName.find(name) == std::string::npos)
 			continue;
 		mtype = mondata.mtype;
@@ -757,14 +757,13 @@ std::string DebugCmdSpawnMonster(const string_view parameter)
 		return "Monster name cannot be empty. Duh.";
 
 	name.pop_back(); // remove last space
-	std::transform(name.begin(), name.end(), name.begin(), [](unsigned char c) { return std::tolower(c); });
+	AsciiStrToLower(name);
 
 	int mtype = -1;
 
 	for (int i = 0; i < NUM_MTYPES; i++) {
 		auto mondata = MonstersData[i];
-		std::string monsterName(mondata.name);
-		std::transform(monsterName.begin(), monsterName.end(), monsterName.begin(), [](unsigned char c) { return std::tolower(c); });
+		const std::string monsterName = AsciiStrToLower(mondata.name);
 		if (monsterName.find(name) == std::string::npos)
 			continue;
 		mtype = i;
@@ -990,7 +989,7 @@ std::string DebugCmdSearchMonster(const string_view parameter)
 
 	std::string name;
 	AppendStrView(name, parameter);
-	std::transform(name.begin(), name.end(), name.begin(), [](unsigned char c) { return std::tolower(c); });
+	AsciiStrToLower(name);
 	SearchMonsters.push_back(name);
 
 	return "We will find this bastard!";
@@ -1005,7 +1004,7 @@ std::string DebugCmdSearchItem(const string_view parameter)
 
 	std::string name;
 	AppendStrView(name, parameter);
-	std::transform(name.begin(), name.end(), name.begin(), [](unsigned char c) { return std::tolower(c); });
+	AsciiStrToLower(name);
 	SearchItems.push_back(name);
 
 	return "Are you greedy? Anyway I will help you.";
@@ -1020,7 +1019,7 @@ std::string DebugCmdSearchObject(const string_view parameter)
 
 	std::string name;
 	AppendStrView(name, parameter);
-	std::transform(name.begin(), name.end(), name.begin(), [](unsigned char c) { return std::tolower(c); });
+	AsciiStrToLower(name);
 	SearchObjects.push_back(name);
 
 	return "I will look for the pyramids. Oh sorry, I'm looking for what you want, of course.";
@@ -1251,11 +1250,9 @@ bool IsDebugAutomapHighlightNeeded()
 bool ShouldHighlightDebugAutomapTile(Point position)
 {
 	auto matchesSearched = [](const string_view name, const std::vector<std::string> &searchedNames) {
-		std::string nameToLower;
-		StrAppend(nameToLower, name);
-		std::transform(nameToLower.begin(), nameToLower.end(), nameToLower.begin(), [](unsigned char c) { return std::tolower(c); });
+		const std::string lowercaseName = AsciiStrToLower(name);
 		for (const auto &searchedName : searchedNames) {
-			if (nameToLower.find(searchedName) != std::string::npos) {
+			if (lowercaseName.find(searchedName) != std::string::npos) {
 				return true;
 			}
 		}
diff --git a/Source/items.cpp b/Source/items.cpp
index 7fc4c77f4..518b685d7 100644
--- a/Source/items.cpp
+++ b/Source/items.cpp
@@ -46,6 +46,7 @@
 #include "utils/log.hpp"
 #include "utils/math.h"
 #include "utils/stdcompat/algorithm.hpp"
+#include "utils/str_case.hpp"
 #include "utils/str_cat.hpp"
 #include "utils/utf8.hpp"
 
@@ -4611,7 +4612,7 @@ std::string DebugSpawnItem(std::string itemName)
 	const int max_time = 3000;
 	const int max_iter = 1000000;
 
-	std::transform(itemName.begin(), itemName.end(), itemName.begin(), [](unsigned char c) { return std::tolower(c); });
+	AsciiStrToLower(itemName);
 
 	Item testItem;
 
@@ -4635,8 +4636,7 @@ std::string DebugSpawnItem(std::string itemName)
 		testItem = {};
 		SetupAllItems(*MyPlayer, testItem, idx, AdvanceRndSeed(), monsterLevel, 1, false, false, false);
 
-		std::string tmp(testItem._iIName);
-		std::transform(tmp.begin(), tmp.end(), tmp.begin(), [](unsigned char c) { return std::tolower(c); });
+		std::string tmp = AsciiStrToLower(testItem._iIName);
 		if (tmp.find(itemName) != std::string::npos)
 			break;
 	}
@@ -4656,7 +4656,7 @@ std::string DebugSpawnUniqueItem(std::string itemName)
 	if (ActiveItemCount >= MAXITEMS)
 		return "No space to generate the item!";
 
-	std::transform(itemName.begin(), itemName.end(), itemName.begin(), [](unsigned char c) { return std::tolower(c); });
+	AsciiStrToLower(itemName);
 	UniqueItem uniqueItem;
 	bool foundUnique = false;
 	int uniqueIndex = 0;
@@ -4664,8 +4664,7 @@ std::string DebugSpawnUniqueItem(std::string itemName)
 		if (!IsUniqueAvailable(j))
 			break;
 
-		std::string tmp(UniqueItems[j].UIName);
-		std::transform(tmp.begin(), tmp.end(), tmp.begin(), [](unsigned char c) { return std::tolower(c); });
+		const std::string tmp = AsciiStrToLower(UniqueItems[j].UIName);
 		if (tmp.find(itemName) != std::string::npos) {
 			itemName = tmp;
 			uniqueItem = UniqueItems[j];
@@ -4718,8 +4717,7 @@ std::string DebugSpawnUniqueItem(std::string itemName)
 		if (testItem._iMagical != ITEM_QUALITY_UNIQUE)
 			continue;
 
-		std::string tmp(testItem._iIName);
-		std::transform(tmp.begin(), tmp.end(), tmp.begin(), [](unsigned char c) { return std::tolower(c); });
+		const std::string tmp = AsciiStrToLower(testItem._iIName);
 		if (tmp.find(itemName) != std::string::npos)
 			break;
 		return "Impossible to generate!";
diff --git a/Source/towners.cpp b/Source/towners.cpp
index a877d009a..37cd6779a 100644
--- a/Source/towners.cpp
+++ b/Source/towners.cpp
@@ -11,6 +11,7 @@
 #include "minitext.h"
 #include "stores.h"
 #include "utils/language.h"
+#include "utils/str_case.hpp"
 
 namespace devilution {
 namespace {
@@ -937,7 +938,7 @@ void UpdateCowFarmerAnimAfterQuestComplete()
 bool DebugTalkToTowner(std::string targetName)
 {
 	SetupTownStores();
-	std::transform(targetName.begin(), targetName.end(), targetName.begin(), [](unsigned char c) { return std::tolower(c); });
+	AsciiStrToLower(targetName);
 	Player &myPlayer = *MyPlayer;
 	for (auto &townerData : TownersData) {
 		if (!IsTownerPresent(townerData.type))
@@ -948,8 +949,7 @@ bool DebugTalkToTowner(std::string targetName)
 		Towner fakeTowner;
 		townerData.init(fakeTowner, townerData);
 		fakeTowner.position = myPlayer.position.tile;
-		std::string npcName(fakeTowner.name);
-		std::transform(npcName.begin(), npcName.end(), npcName.begin(), [](unsigned char c) { return std::tolower(c); });
+		const std::string npcName = AsciiStrToLower(fakeTowner.name);
 		if (npcName.find(targetName) != std::string::npos) {
 			townerData.talk(myPlayer, fakeTowner);
 			return true;
diff --git a/Source/utils/str_case.cpp b/Source/utils/str_case.cpp
new file mode 100644
index 000000000..4ca9e2083
--- /dev/null
+++ b/Source/utils/str_case.cpp
@@ -0,0 +1,13 @@
+#include "utils/str_case.hpp"
+
+namespace devilution {
+
+void AsciiStrToLower(std::string &str)
+{
+	for (char &c : str) { // NOLINT(readability-identifier-length)
+		if (c >= 'A' && c <= 'Z')
+			c += ('a' - 'A');
+	}
+}
+
+} // namespace devilution
diff --git a/Source/utils/str_case.hpp b/Source/utils/str_case.hpp
new file mode 100644
index 000000000..59564c4ab
--- /dev/null
+++ b/Source/utils/str_case.hpp
@@ -0,0 +1,18 @@
+#pragma once
+
+#include <string>
+
+#include "utils/stdcompat/string_view.hpp"
+
+namespace devilution {
+
+void AsciiStrToLower(std::string &str);
+
+[[nodiscard]] inline std::string AsciiStrToLower(string_view str)
+{
+	std::string copy { str.data(), str.size() };
+	AsciiStrToLower(copy);
+	return copy;
+}
+
+} // namespace devilution