diff --git a/random.c b/random.c
index 3be22a4ec0..1093a103c1 100644
--- a/random.c
+++ b/random.c
@@ -991,7 +991,11 @@ random_ulong_limited(VALUE obj, rb_random_t *rnd, unsigned long limit)
 	const int w = sizeof(limit) * CHAR_BIT - nlz_long(limit);
 	const int n = w > 32 ? sizeof(unsigned long) : sizeof(uint32_t);
 	const unsigned long mask = ~(~0UL << w);
-	const unsigned long full = ~(~0UL << n * CHAR_BIT);
+	const unsigned long full =
+#if SIZEOF_LONG == 4
+	    (size_t)n >= sizeof(unsigned long) ? ~0UL :
+#endif
+	    ~(~0UL << n * CHAR_BIT);
 	unsigned long val, bits = 0, rest = 0;
 	do {
 	    if (mask & ~rest) {