diff --git a/Objects/codeobject.c b/Objects/codeobject.c
index 0d9e5d16e76..63ce4793597 100644
--- a/Objects/codeobject.c
+++ b/Objects/codeobject.c
@@ -261,7 +261,8 @@ _PyCode_InitOpcache(PyCodeObject *co)
 
         // TODO: LOAD_METHOD, LOAD_ATTR
         if (opcode == LOAD_GLOBAL) {
-            co->co_opcache_map[i] = ++opts;
+            opts++;
+            co->co_opcache_map[i] = (unsigned char)opts;
             if (opts > 254) {
                 break;
             }