diff --git a/doc/crypto/hmac.pod b/doc/crypto/hmac.pod
index 3976baf22..0bd79a6d3 100644
--- a/doc/crypto/hmac.pod
+++ b/doc/crypto/hmac.pod
@@ -18,7 +18,7 @@ authentication code
  void HMAC_Init(HMAC_CTX *ctx, const void *key, int key_len,
                const EVP_MD *md);
  void HMAC_Init_ex(HMAC_CTX *ctx, const void *key, int key_len,
-               	   const EVP_MD *md);
+               	   const EVP_MD *md, ENGINE *impl);
  void HMAC_Update(HMAC_CTX *ctx, const unsigned char *data, int len);
  void HMAC_Final(HMAC_CTX *ctx, unsigned char *md, unsigned int *len);