diff --git a/crypto/hmac/hmac.c b/crypto/hmac/hmac.c
index 9504aada943bd337f7fef851c5de82f7325f2626..4e09e56f1545de425d2369e18a5778b2c312109f 100644
--- a/crypto/hmac/hmac.c
+++ b/crypto/hmac/hmac.c
@@ -164,7 +164,7 @@ int HMAC_Final(HMAC_CTX *ctx, unsigned char *md, unsigned int *len)
     return 0;
 }
 
-size_t HMAC_size(HMAC_CTX *ctx)
+size_t HMAC_size(const HMAC_CTX *ctx)
 {
     return EVP_MD_size((ctx)->md);
 }
diff --git a/include/openssl/hmac.h b/include/openssl/hmac.h
index 71d7d6591623c5bacb8218743ad238816dbe14f4..88ebf0d3e4031e02176947dbcfd0c7c066e49521 100644
--- a/include/openssl/hmac.h
+++ b/include/openssl/hmac.h
@@ -67,7 +67,7 @@
 extern "C" {
 #endif
 
-size_t HMAC_size(HMAC_CTX *e);
+size_t HMAC_size(const HMAC_CTX *e);
 HMAC_CTX *HMAC_CTX_new(void);
 int HMAC_CTX_reset(HMAC_CTX *ctx);
 void HMAC_CTX_free(HMAC_CTX *ctx);