diff --git a/library/ecdsa.c b/library/ecdsa.c
index 7dc8708..7f259e1 100644
--- a/library/ecdsa.c
+++ b/library/ecdsa.c
@@ -870,8 +870,8 @@
 
     if( p + len != end )
     {
-        ret = MBEDTLS_ERR_ECP_BAD_INPUT_DATA +
-              MBEDTLS_ERR_ASN1_LENGTH_MISMATCH;
+        ret = MBEDTLS_ERROR_ADD( MBEDTLS_ERR_ECP_BAD_INPUT_DATA,
+              MBEDTLS_ERR_ASN1_LENGTH_MISMATCH );
         goto cleanup;
     }