diff --git a/library/chachapoly.c b/library/chachapoly.c
index 9ca21b3..fd05886 100644
--- a/library/chachapoly.c
+++ b/library/chachapoly.c
@@ -202,7 +202,7 @@
                                const unsigned char *input,
                                unsigned char *output )
 {
-    if ( ( ctx == NULL ) || ( input == NULL ) || ( output == NULL ) )
+    if ( ctx == NULL )
     {
         return( MBEDTLS_ERR_CHACHAPOLY_BAD_INPUT_DATA );
     }
@@ -339,6 +339,9 @@
     size_t i;
     int diff;
 
+    if( tag == NULL )
+        return( MBEDTLS_ERR_CHACHAPOLY_BAD_INPUT_DATA );
+
     if( ( ret = mbedtls_chachapoly_crypt_and_tag( ctx,
                         MBEDTLS_CHACHAPOLY_DECRYPT, length, nonce,
                         aad, aad_len, input, output, check_tag ) ) != 0 )