diff --git a/servers/rendering/shader_language.cpp b/servers/rendering/shader_language.cpp
index 1a4c8ea742a0..9aa54d0bb775 100644
--- a/servers/rendering/shader_language.cpp
+++ b/servers/rendering/shader_language.cpp
@@ -3067,6 +3067,8 @@ const ShaderLanguage::BuiltinFuncDef ShaderLanguage::builtin_func_defs[] = {
 	{ nullptr, TYPE_VOID, { TYPE_VOID }, { "" }, TAG_GLOBAL, false }
 };
 
+HashSet<StringName> global_func_set;
+
 const ShaderLanguage::BuiltinFuncOutArgs ShaderLanguage::builtin_func_out_args[] = {
 	{ "modf", { 1, -1 } },
 	{ "umulExtended", { 2, 3 } },
@@ -9211,7 +9213,7 @@ Error ShaderLanguage::_parse_shader(const HashMap<StringName, FunctionInfo> &p_f
 					return ERR_PARSE_ERROR;
 				}
 
-				if (shader->structs.has(name) || _find_identifier(nullptr, false, constants, name) || has_builtin(p_functions, name)) {
+				if (shader->structs.has(name) || _find_identifier(nullptr, false, constants, name) || has_builtin(p_functions, name, !is_constant)) {
 					_set_redefinition_error(String(name));
 					return ERR_PARSE_ERROR;
 				}
@@ -9831,7 +9833,11 @@ Error ShaderLanguage::_parse_shader(const HashMap<StringName, FunctionInfo> &p_f
 	return OK;
 }
 
-bool ShaderLanguage::has_builtin(const HashMap<StringName, ShaderLanguage::FunctionInfo> &p_functions, const StringName &p_name) {
+bool ShaderLanguage::has_builtin(const HashMap<StringName, ShaderLanguage::FunctionInfo> &p_functions, const StringName &p_name, bool p_check_global_funcs) {
+	if (p_check_global_funcs && global_func_set.has(p_name)) {
+		return true;
+	}
+
 	for (const KeyValue<StringName, ShaderLanguage::FunctionInfo> &E : p_functions) {
 		if (E.value.built_ins.has(p_name)) {
 			return true;
@@ -10701,6 +10707,18 @@ ShaderLanguage::ShaderLanguage() {
 	nodes = nullptr;
 	completion_class = TAG_GLOBAL;
 
+	int idx = 0;
+	while (builtin_func_defs[idx].name) {
+		if (builtin_func_defs[idx].tag == SubClassTag::TAG_GLOBAL) {
+			const StringName &name = StringName(builtin_func_defs[idx].name);
+
+			if (!global_func_set.has(name)) {
+				global_func_set.insert(name);
+			}
+		}
+		idx++;
+	}
+
 #ifdef DEBUG_ENABLED
 	warnings_check_map.insert(ShaderWarning::UNUSED_CONSTANT, &used_constants);
 	warnings_check_map.insert(ShaderWarning::UNUSED_FUNCTION, &used_functions);
diff --git a/servers/rendering/shader_language.h b/servers/rendering/shader_language.h
index 38f304ff31a5..5615d7f457fd 100644
--- a/servers/rendering/shader_language.h
+++ b/servers/rendering/shader_language.h
@@ -884,7 +884,7 @@ public:
 		bool can_discard = false;
 		bool main_function = false;
 	};
-	static bool has_builtin(const HashMap<StringName, ShaderLanguage::FunctionInfo> &p_functions, const StringName &p_name);
+	static bool has_builtin(const HashMap<StringName, ShaderLanguage::FunctionInfo> &p_functions, const StringName &p_name, bool p_check_global_funcs = false);
 
 	typedef DataType (*GlobalShaderUniformGetTypeFunc)(const StringName &p_name);