diff --git a/include/openssl/bytestring.h b/include/openssl/bytestring.h
index 631acdd..544a5d5 100644
--- a/include/openssl/bytestring.h
+++ b/include/openssl/bytestring.h
@@ -73,6 +73,11 @@
  * a NUL byte and zero otherwise. */
 int CBS_contains_zero_byte(const CBS *cbs);
 
+/* CBS_mem_equal compares the current contents of |cbs| with the |len| bytes
+ * starting at |data|. If they're equal, it returns one, otherwise zero. If the
+ * lengths match, it uses a constant-time comparison. */
+int CBS_mem_equal(const CBS *cbs, const uint8_t *data, size_t len);
+
 /* CBS_get_u8 sets |*out| to the next uint8_t from |cbs| and advances |cbs|. It
  * returns one on success and zero on error. */
 int CBS_get_u8(CBS *cbs, uint8_t *out);