diff --git a/upb/port/def.inc b/upb/port/def.inc
index 526ab0871d90..bdd4d6f0a128 100644
--- a/upb/port/def.inc
+++ b/upb/port/def.inc
@@ -68,10 +68,10 @@ Error, UINTPTR_MAX is undefined
 // overall - in that case, it can overlap with the trailing padding of the rest
 // of the struct, and a naive sizeof(base) + sizeof(flex) * count calculation
 // will not take into account that overlap, and allocate more than is required.
-#define UPB_SIZEOF_FLEX(type, member, count) \
-  (UPB_MAX(sizeof(type),                     \
-           (offsetof(type, member) +         \
-            count * (offsetof(type, member[1]) - offsetof(type, member[0])))))
+#define UPB_SIZEOF_FLEX(type, member, count)                                \
+  (UPB_MAX(sizeof(type),                                                    \
+           (offsetof(type, member) + (count) * (offsetof(type, member[1]) - \
+                                                offsetof(type, member[0])))))
 
 #define UPB_MAPTYPE_STRING 0