diff --git a/py/parse.c b/py/parse.c
index 82b5413e59..42a947997a 100644
--- a/py/parse.c
+++ b/py/parse.c
@@ -208,7 +208,7 @@ STATIC const char *const rule_name_table[] = {
 #endif
 
 typedef struct _rule_stack_t {
-    size_t src_line : 8 * sizeof(size_t) - 8; // maximum bits storing source line number
+    size_t src_line : (8 * sizeof(size_t) - 8); // maximum bits storing source line number
     size_t rule_id : 8; // this must be large enough to fit largest rule number
     size_t arg_i; // this dictates the maximum nodes in a "list" of things
 } rule_stack_t;