diff --git a/src/scripting/thingdef_data.cpp b/src/scripting/thingdef_data.cpp
index f7b84f21b..274c865bf 100644
--- a/src/scripting/thingdef_data.cpp
+++ b/src/scripting/thingdef_data.cpp
@@ -1267,3 +1267,16 @@ DEFINE_ACTION_FUNCTION(FStringStruct, LastIndexOf)
 	ACTION_RETURN_INT(self->LastIndexOf(substr));
 }
 
+DEFINE_ACTION_FUNCTION(FStringStruct, ToUpper)
+{
+	PARAM_SELF_STRUCT_PROLOGUE(FString);
+	self->ToUpper();
+	return 0;
+}
+
+DEFINE_ACTION_FUNCTION(FStringStruct, ToLower)
+{
+	PARAM_SELF_STRUCT_PROLOGUE(FString);
+	self->ToLower();
+	return 0;
+}
diff --git a/wadsrc/static/zscript/base.txt b/wadsrc/static/zscript/base.txt
index b2fd9c6c8..b7607d555 100644
--- a/wadsrc/static/zscript/base.txt
+++ b/wadsrc/static/zscript/base.txt
@@ -658,6 +658,8 @@ struct StringStruct native
 	native String Filter();
 	native int IndexOf(String substr, int startIndex = 0) const;
 	native int LastIndexOf(String substr) const;
+	native void ToUpper();
+	native void ToLower();
 }
 
 class SectorEffect : Thinker native