diff --git a/library/psa_crypto.c b/library/psa_crypto.c
index 45f5563..5810853 100755
--- a/library/psa_crypto.c
+++ b/library/psa_crypto.c
@@ -1488,7 +1488,7 @@
     size_t key_bits;
     unsigned char tag[16];
     mbedtls_cipher_id_t cipher_id;
-    
+
     if( ciphertext_size < ( plaintext_length + sizeof( tag ) ) )
             return( PSA_ERROR_INVALID_ARGUMENT );
 
@@ -1508,9 +1508,8 @@
 
     //TODO: check key policy
 
-
-    if ( ( key_type & PSA_KEY_TYPE_CATEGORY_MASK ) == PSA_KEY_TYPE_CATEGORY_CIPHER
-           && PSA_BLOCK_CIPHER_BLOCK_SIZE( key_type ) == 16 )
+    if ( !( ( key_type & PSA_KEY_TYPE_CATEGORY_MASK ) == PSA_KEY_TYPE_CATEGORY_CIPHER
+           && PSA_BLOCK_CIPHER_BLOCK_SIZE( key_type ) == 16 ) )
         return( PSA_ERROR_INVALID_ARGUMENT );
 
     if( alg == PSA_ALG_GCM )
@@ -1609,9 +1608,8 @@
 
     //TODO: check key policy
 
-
-    if ( ( key_type & PSA_KEY_TYPE_CATEGORY_MASK ) == PSA_KEY_TYPE_CATEGORY_CIPHER
-           && PSA_BLOCK_CIPHER_BLOCK_SIZE( key_type ) == 16 )
+    if ( !( ( key_type & PSA_KEY_TYPE_CATEGORY_MASK ) == PSA_KEY_TYPE_CATEGORY_CIPHER
+           && PSA_BLOCK_CIPHER_BLOCK_SIZE( key_type ) == 16 ) )
         return( PSA_ERROR_INVALID_ARGUMENT );
 
     if( alg == PSA_ALG_GCM )