diff --git a/library/pkparse.c b/library/pkparse.c
index f97d89ea14..491cecf50f 100644
--- a/library/pkparse.c
+++ b/library/pkparse.c
@@ -1274,6 +1274,9 @@ int mbedtls_pk_parse_key( mbedtls_pk_context *pk,
     {
         unsigned char *key_copy;
 
+        if( keylen == 0 )
+            return( MBEDTLS_ERR_PK_KEY_INVALID_FORMAT );
+
         if( ( key_copy = mbedtls_calloc( 1, keylen ) ) == NULL )
             return( MBEDTLS_ERR_PK_ALLOC_FAILED );