diff --git a/library/cipher.c b/library/cipher.c
index e9e0b22..ff03273 100644
--- a/library/cipher.c
+++ b/library/cipher.c
@@ -516,14 +516,14 @@
     if( NULL == input || NULL == data_len )
         return( MBEDTLS_ERR_CIPHER_BAD_INPUT_DATA );
 
-    bad = 0xFF;
+    bad = 0x80;
     *data_len = 0;
     for( i = input_len; i > 0; i-- )
     {
         prev_done = done;
-        done |= ( input[i-1] != 0 );
+        done |= ( input[i - 1] != 0 );
         *data_len |= ( i - 1 ) * ( done != prev_done );
-        bad &= ( input[i-1] ^ 0x80 ) | ( done == prev_done );
+        bad ^= input[i - 1] * ( done != prev_done );
     }
 
     return( MBEDTLS_ERR_CIPHER_INVALID_PADDING * ( bad != 0 ) );