diff --git a/include/polarssl/des.h b/include/polarssl/des.h
index 5606afbe7..09c00a741 100644
--- a/include/polarssl/des.h
+++ b/include/polarssl/des.h
@@ -77,14 +77,17 @@ void des_key_set_parity( unsigned char key[DES_KEY_SIZE] );
  *                 a parity bit to allow verification.
  *
  * \param key      8-byte secret key
+ *
+ * \return         0 is parity was ok, 1 if parity was not correct.
  */
 int des_key_check_key_parity( const unsigned char key[DES_KEY_SIZE] );
 
-
 /**
  * \brief          Check that key is not a weak or semi-weak DES key
  *
  * \param key      8-byte secret key
+ *
+ * \resurn         0 if no weak key was found, 1 if a weak key was identified.
  */
 int des_key_check_weak( const unsigned char key[DES_KEY_SIZE] );
 
diff --git a/library/des.c b/library/des.c
index 303403082..b40baf8fb 100644
--- a/library/des.c
+++ b/library/des.c
@@ -371,9 +371,9 @@ int des_key_check_weak( const unsigned char key[DES_KEY_SIZE] )
 
     for( i = 0; i < WEAK_KEY_COUNT; i++ )
         if( memcmp( weak_key_table[i], key, DES_KEY_SIZE) == 0)
-            return( 0 );
+            return( 1 );
 
-    return( 1 );
+    return( 0 );
 }
 
 static void des_setkey( unsigned long SK[32], const unsigned char key[DES_KEY_SIZE] )