diff --git a/libc/include/sys/cdefs.h b/libc/include/sys/cdefs.h
index 7df8b60..8a11bc6 100644
--- a/libc/include/sys/cdefs.h
+++ b/libc/include/sys/cdefs.h
@@ -578,4 +578,19 @@
 #define _BIONIC_NOT_BEFORE_21(x)
 #endif /* __ANDROID_API__ >= 21 */
 
+#if __has_builtin(__builtin_umul_overflow) || __GNUC__ >= 5
+#if __LP64__
+#define __size_mul_overflow(a, b, result) __builtin_umull_overflow(a, b, result)
+#else
+#define __size_mul_overflow(a, b, result) __builtin_umul_overflow(a, b, result)
+#endif
+#else
+static __inline__ __always_inline int __size_mul_overflow(__SIZE_TYPE__ a, __SIZE_TYPE__ b,
+                                                          __SIZE_TYPE__ *result) {
+    *result = a * b;
+    static const __SIZE_TYPE__ mul_no_overflow = 1UL << (sizeof(__SIZE_TYPE__) * 4);
+    return (a >= mul_no_overflow || b >= mul_no_overflow) && a > 0 && (__SIZE_TYPE__)-1 / a < b;
+}
+#endif
+
 #endif /* !_SYS_CDEFS_H_ */