diff --git a/Slang/builtin.h b/Slang/builtin.h
index 417655e..10e5e88 100644
--- a/Slang/builtin.h
+++ b/Slang/builtin.h
@@ -112,6 +112,8 @@ any CPPFunction(string name, vector<any> args)
 		cout << AnyAsString(args[0]);
 	else if (name == "CPP.System.PrintLine")
 		cout << AnyAsString(args[0]) << endl;
+	else
+		LogWarning("CPP function \'" + name + "\' does not exist.")
 
 	return 0;
 }