diff --git a/library/psa_crypto.c b/library/psa_crypto.c
index ba1fd9d..a8306ab 100755
--- a/library/psa_crypto.c
+++ b/library/psa_crypto.c
@@ -1656,8 +1656,8 @@
     if( !( slot->policy.usage & PSA_KEY_USAGE_DECRYPT ) )
         return( PSA_ERROR_NOT_PERMITTED );
 
-    if ( !( ( key_type & PSA_KEY_TYPE_CATEGORY_MASK ) ==
-            PSA_KEY_TYPE_CATEGORY_SYMMETRIC )
+    if ( ( key_type & PSA_KEY_TYPE_CATEGORY_MASK ) != 
+         PSA_KEY_TYPE_CATEGORY_SYMMETRIC )
         return( PSA_ERROR_INVALID_ARGUMENT );
 
     if( alg == PSA_ALG_GCM )