diff --git a/src/scripting/zscript/zcc_compile.cpp b/src/scripting/zscript/zcc_compile.cpp
index d782383e7..ccfb1f75e 100644
--- a/src/scripting/zscript/zcc_compile.cpp
+++ b/src/scripting/zscript/zcc_compile.cpp
@@ -2533,6 +2533,11 @@ void ZCCCompiler::CompileFunction(ZCC_StructWork *c, ZCC_FuncDeclarator *f, bool
 					}
 					else if (p->Default != nullptr)
 					{
+						if (flags & VARF_Out)
+						{
+							Error(p, "Out parameters cannot have default values");
+						}
+
 						flags |= VARF_Optional;
 						hasoptionals = true;