diff --git a/crypto/cryptlib.c b/crypto/cryptlib.c
index c9f674ba8..1925428f5 100644
--- a/crypto/cryptlib.c
+++ b/crypto/cryptlib.c
@@ -1016,11 +1016,11 @@ void *OPENSSL_stderr(void)
     return stderr;
 }
 
-int CRYPTO_memcmp(const void *in_a, const void *in_b, size_t len)
+int CRYPTO_memcmp(const volatile void *in_a, const volatile void *in_b, size_t len)
 {
     size_t i;
-    const unsigned char *a = in_a;
-    const unsigned char *b = in_b;
+    const volatile unsigned char *a = in_a;
+    const volatile unsigned char *b = in_b;
     unsigned char x = 0;
 
     for (i = 0; i < len; i++)
diff --git a/crypto/crypto.h b/crypto/crypto.h
index c450d7a3c..6c644ce12 100644
--- a/crypto/crypto.h
+++ b/crypto/crypto.h
@@ -628,7 +628,7 @@ void OPENSSL_init(void);
  * into a defined order as the return value when a != b is undefined, other
  * than to be non-zero.
  */
-int CRYPTO_memcmp(const void *a, const void *b, size_t len);
+int CRYPTO_memcmp(const volatile void *a, const volatile void *b, size_t len);
 
 /* BEGIN ERROR CODES */
 /*