diff --git a/include/mbedtls/cmac.h b/include/mbedtls/cmac.h
index 6d531dddb..71f7ab43a 100644
--- a/include/mbedtls/cmac.h
+++ b/include/mbedtls/cmac.h
@@ -69,7 +69,7 @@ struct mbedtls_cmac_context_t
  * \return              0 if successful, or a cipher specific error code
  */
 int mbedtls_cipher_cmac_starts( mbedtls_cipher_context_t *ctx,
-                                const unsigned char *key, size_t keylen );
+                                const unsigned char *key, size_t keybits );
 
 /**
  * \brief               Generic CMAC process buffer.
diff --git a/library/cmac.c b/library/cmac.c
index 1eb1c1074..5a6206ea9 100644
--- a/library/cmac.c
+++ b/library/cmac.c
@@ -201,7 +201,7 @@ static void cmac_pad( unsigned char padded_block[16],
 }
 
 int mbedtls_cipher_cmac_starts( mbedtls_cipher_context_t *ctx,
-                                const unsigned char *key, size_t keylen )
+                                const unsigned char *key, size_t keybits )
 {
     mbedtls_cipher_type_t type;
     mbedtls_cmac_context_t *cmac_ctx;
@@ -211,7 +211,7 @@ int mbedtls_cipher_cmac_starts( mbedtls_cipher_context_t *ctx,
     if( ctx == NULL || ctx->cipher_info == NULL || key == NULL )
         return( MBEDTLS_ERR_CIPHER_BAD_INPUT_DATA );
 
-    if( ( retval = mbedtls_cipher_setkey( ctx, key, keylen,
+    if( ( retval = mbedtls_cipher_setkey( ctx, key, keybits,
                                           MBEDTLS_ENCRYPT ) ) != 0 )
         return( retval );