diff --git a/tools/qfcc/source/function.c b/tools/qfcc/source/function.c
index 098d0ae9e..3727b1c02 100644
--- a/tools/qfcc/source/function.c
+++ b/tools/qfcc/source/function.c
@@ -219,6 +219,10 @@ build_builtin_function (def_t *def, expr_t *bi_val)
 		error (bi_val, "%s is not a function", def->name);
 		return 0;
 	}
+	if (def->constant) {
+		error (bi_val, "%s redefined", def->name);
+		return 0;
+	}
 
 	if (bi_val->type != ex_integer && bi_val->type != ex_float) {
 		error (bi_val, "invalid constant for = #");
diff --git a/tools/qfcc/source/qc-parse.y b/tools/qfcc/source/qc-parse.y
index 3c3ce1658..06b587891 100644
--- a/tools/qfcc/source/qc-parse.y
+++ b/tools/qfcc/source/qc-parse.y
@@ -624,6 +624,8 @@ opt_comma
 begin_function
 	: /*empty*/
 		{
+			if ($<def>0->constant)
+				error (0, "%s redefined", $<def>0->name);
 			$$ = current_func = new_function ($<def>0->name);
 			$$->def = $<def>0;
 			$$->refs = new_reloc ($$->def->ofs, rel_def_func);