diff --git a/src/ObjLoading/Game/IW4/Menu/MenuConverterIW4.cpp b/src/ObjLoading/Game/IW4/Menu/MenuConverterIW4.cpp
index 6aa08ac60..a2cae9a82 100644
--- a/src/ObjLoading/Game/IW4/Menu/MenuConverterIW4.cpp
+++ b/src/ObjLoading/Game/IW4/Menu/MenuConverterIW4.cpp
@@ -12,6 +12,7 @@
 #include "Parsing/Simple/Expression/SimpleExpressionConditionalOperator.h"
 #include "Parsing/Simple/Expression/SimpleExpressionUnaryOperation.h"
 #include "Utils/ClassUtils.h"
+#include "Utils/StringUtils.h"
 
 #include <cassert>
 #include <cstring>
@@ -204,12 +205,15 @@ namespace IW4
                                                       const CommonMenuDef* menu,
                                                       const CommonItemDef* item) const
         {
-            Statement_s* functionStatement = m_conversion_zone_state->FindFunction(functionCall->m_function_name);
+            std::string lowerCaseFunctionName(functionCall->m_function_name);
+            utils::MakeStringLowerCase(lowerCaseFunctionName);
+
+            Statement_s* functionStatement = m_conversion_zone_state->FindFunction(lowerCaseFunctionName);
 
             if (functionStatement == nullptr)
             {
                 // Function was not converted yet: Convert it now
-                const auto foundCommonFunction = m_parsing_zone_state->m_functions_by_name.find(functionCall->m_function_name);
+                const auto foundCommonFunction = m_parsing_zone_state->m_functions_by_name.find(lowerCaseFunctionName);
 
                 if (foundCommonFunction == m_parsing_zone_state->m_functions_by_name.end())
                     throw MenuConversionException("Failed to find definition for custom function \"" + functionCall->m_function_name + "\"", menu, item);
diff --git a/src/ObjLoading/Game/IW5/Menu/MenuConverterIW5.cpp b/src/ObjLoading/Game/IW5/Menu/MenuConverterIW5.cpp
index 2da2a9da3..321146fcc 100644
--- a/src/ObjLoading/Game/IW5/Menu/MenuConverterIW5.cpp
+++ b/src/ObjLoading/Game/IW5/Menu/MenuConverterIW5.cpp
@@ -12,6 +12,7 @@
 #include "Parsing/Simple/Expression/SimpleExpressionConditionalOperator.h"
 #include "Parsing/Simple/Expression/SimpleExpressionUnaryOperation.h"
 #include "Utils/ClassUtils.h"
+#include "Utils/StringUtils.h"
 
 #include <cassert>
 #include <cstring>
@@ -204,18 +205,21 @@ namespace IW5
                                                       const CommonMenuDef* menu,
                                                       const CommonItemDef* item) const
         {
-            Statement_s* functionStatement = m_conversion_zone_state->FindFunction(functionCall->m_function_name);
+            std::string lowerCaseFunctionName(functionCall->m_function_name);
+            utils::MakeStringLowerCase(lowerCaseFunctionName);
+
+            Statement_s* functionStatement = m_conversion_zone_state->FindFunction(lowerCaseFunctionName);
 
             if (functionStatement == nullptr)
             {
                 // Function was not converted yet: Convert it now
-                const auto foundCommonFunction = m_parsing_zone_state->m_functions_by_name.find(functionCall->m_function_name);
+                const auto foundCommonFunction = m_parsing_zone_state->m_functions_by_name.find(lowerCaseFunctionName);
 
                 if (foundCommonFunction == m_parsing_zone_state->m_functions_by_name.end())
                     throw MenuConversionException("Failed to find definition for custom function \"" + functionCall->m_function_name + "\"", menu, item);
 
                 functionStatement = ConvertExpression(foundCommonFunction->second->m_value.get(), menu, item);
-                functionStatement = m_conversion_zone_state->AddFunction(foundCommonFunction->second->m_name, functionStatement);
+                functionStatement = m_conversion_zone_state->AddFunction(lowerCaseFunctionName, functionStatement);
             }
 
             expressionEntry functionEntry{};
diff --git a/src/ObjLoading/Parsing/Menu/Matcher/MenuExpressionMatchers.cpp b/src/ObjLoading/Parsing/Menu/Matcher/MenuExpressionMatchers.cpp
index 9ec73c373..b5acb8acc 100644
--- a/src/ObjLoading/Parsing/Menu/Matcher/MenuExpressionMatchers.cpp
+++ b/src/ObjLoading/Parsing/Menu/Matcher/MenuExpressionMatchers.cpp
@@ -58,7 +58,11 @@ const std::map<std::string, size_t>& MenuExpressionMatchers::GetBaseFunctionMapF
         if (!iw4FunctionMapInitialized)
         {
             for (size_t i = IW4::expressionFunction_e::EXP_FUNC_DYN_START; i < std::extent_v<decltype(IW4::g_expFunctionNames)>; i++)
-                iw4FunctionMap.emplace(std::make_pair(IW4::g_expFunctionNames[i], i));
+            {
+                std::string functionName(IW4::g_expFunctionNames[i]);
+                utils::MakeStringLowerCase(functionName);
+                iw4FunctionMap.emplace(std::make_pair(functionName, i));
+            }
         }
 
         return iw4FunctionMap;
@@ -71,7 +75,11 @@ const std::map<std::string, size_t>& MenuExpressionMatchers::GetBaseFunctionMapF
         if (!iw5FunctionMapInitialized)
         {
             for (size_t i = IW5::expressionFunction_e::EXP_FUNC_DYN_START; i < std::extent_v<decltype(IW5::g_expFunctionNames)>; i++)
-                iw5FunctionMap.emplace(std::make_pair(IW5::g_expFunctionNames[i], i));
+            {
+                std::string functionName(IW5::g_expFunctionNames[i]);
+                utils::MakeStringLowerCase(functionName);
+                iw5FunctionMap.emplace(std::make_pair(std::move(functionName), i));
+            }
         }
 
         return iw5FunctionMap;
diff --git a/src/ObjLoading/Parsing/Menu/MenuAssetZoneState.cpp b/src/ObjLoading/Parsing/Menu/MenuAssetZoneState.cpp
index 0b3a8eb9c..cf9c5191b 100644
--- a/src/ObjLoading/Parsing/Menu/MenuAssetZoneState.cpp
+++ b/src/ObjLoading/Parsing/Menu/MenuAssetZoneState.cpp
@@ -1,10 +1,15 @@
 #include "MenuAssetZoneState.h"
 
+#include "Utils/StringUtils.h"
+
 using namespace menu;
 
 void MenuAssetZoneState::AddFunction(std::unique_ptr<CommonFunctionDef> function)
 {
-    m_functions_by_name.emplace(std::make_pair(function->m_name, function.get()));
+    std::string lowerCaseFunctionName(function->m_name);
+    utils::MakeStringLowerCase(lowerCaseFunctionName);
+
+    m_functions_by_name.emplace(std::make_pair(lowerCaseFunctionName, function.get()));
     m_functions.emplace_back(std::move(function));
 }
 
diff --git a/src/ObjLoading/Parsing/Menu/MenuFileParserState.cpp b/src/ObjLoading/Parsing/Menu/MenuFileParserState.cpp
index 64fe0ffa9..9cb3af8ac 100644
--- a/src/ObjLoading/Parsing/Menu/MenuFileParserState.cpp
+++ b/src/ObjLoading/Parsing/Menu/MenuFileParserState.cpp
@@ -1,5 +1,7 @@
 #include "MenuFileParserState.h"
 
+#include "Utils/StringUtils.h"
+
 using namespace menu;
 
 MenuFileParserState::EventHandlerConditionState::EventHandlerConditionState(CommonEventHandlerCondition* condition)
@@ -32,7 +34,9 @@ MenuFileParserState::MenuFileParserState(const FeatureLevel featureLevel, const
 {
     for (const auto& function : zoneState->m_functions)
     {
-        m_functions_by_name.emplace(std::make_pair(function->m_name, function.get()));
+        std::string lowerCaseName(function->m_name);
+        utils::MakeStringLowerCase(lowerCaseName);
+        m_functions_by_name.emplace(std::make_pair(lowerCaseName, function.get()));
     }
 
     for (const auto& menu : zoneState->m_menus)
diff --git a/src/ObjLoading/Parsing/Menu/MenuFileParserState.h b/src/ObjLoading/Parsing/Menu/MenuFileParserState.h
index 7eedb75c5..719465241 100644
--- a/src/ObjLoading/Parsing/Menu/MenuFileParserState.h
+++ b/src/ObjLoading/Parsing/Menu/MenuFileParserState.h
@@ -36,7 +36,9 @@ namespace menu
         std::vector<std::unique_ptr<CommonFunctionDef>> m_functions;
         std::vector<std::unique_ptr<CommonMenuDef>> m_menus;
 
+        // Function names are case-insensitive, therefore keys are always lowercase
         std::map<std::string, CommonFunctionDef*> m_functions_by_name;
+
         std::map<std::string, CommonMenuDef*> m_menus_by_name;
 
         bool m_in_global_scope;
diff --git a/src/ObjLoading/Parsing/Menu/Sequence/FunctionScopeSequences.cpp b/src/ObjLoading/Parsing/Menu/Sequence/FunctionScopeSequences.cpp
index 5459a3dd6..45655f96a 100644
--- a/src/ObjLoading/Parsing/Menu/Sequence/FunctionScopeSequences.cpp
+++ b/src/ObjLoading/Parsing/Menu/Sequence/FunctionScopeSequences.cpp
@@ -34,10 +34,13 @@ namespace menu::function_scope_sequences
                 throw ParsingException(result.NextCapture(CAPTURE_TOKEN).GetPos(), ss.str());
             }
 
-            const auto existingFunction = state->m_functions_by_name.find(state->m_current_function->m_name);
+            auto lowerCaseName = state->m_current_function->m_name;
+            utils::MakeStringLowerCase(lowerCaseName);
+
+            const auto existingFunction = state->m_functions_by_name.find(lowerCaseName);
             if (existingFunction == state->m_functions_by_name.end())
             {
-                state->m_functions_by_name.emplace(std::make_pair(state->m_current_function->m_name, state->m_current_function));
+                state->m_functions_by_name.emplace(std::make_pair(lowerCaseName, state->m_current_function));
                 state->m_current_function = nullptr;
             }
             else if (!state->m_current_function->m_value->Equals(existingFunction->second->m_value.get()))