diff --git a/library/poly1305.c b/library/poly1305.c
index 542a850..0aa4533 100644
--- a/library/poly1305.c
+++ b/library/poly1305.c
@@ -259,7 +259,7 @@
 int mbedtls_poly1305_starts( mbedtls_poly1305_context *ctx,
                              const unsigned char key[32] )
 {
-    if ( ctx == NULL )
+    if ( ctx == NULL || key == NULL )
     {
         return( MBEDTLS_ERR_POLY1305_BAD_INPUT_DATA );
     }
@@ -417,7 +417,7 @@
 
 cleanup:
     mbedtls_poly1305_free( &ctx );
-    return( 0 );
+    return( result );
 }
 
 #endif /* MBEDTLS_POLY1305_ALT */