diff --git a/Objects/obmalloc.c b/Objects/obmalloc.c
index 2f2b35e..efbd566 100644
--- a/Objects/obmalloc.c
+++ b/Objects/obmalloc.c
@@ -526,9 +526,9 @@
 		numarenas = maxarenas ? maxarenas << 1 : INITIAL_ARENA_OBJECTS;
 		if (numarenas <= maxarenas)
 			return NULL;	/* overflow */
-		nbytes = numarenas * sizeof(*arenas);
-		if (nbytes / sizeof(*arenas) != numarenas)
+		if (numarenas > PY_SIZE_MAX / sizeof(*arenas))
 			return NULL;	/* overflow */
+		nbytes = numarenas * sizeof(*arenas);
 		arenaobj = (struct arena_object *)realloc(arenas, nbytes);
 		if (arenaobj == NULL)
 			return NULL;