diff --git a/library/psa_crypto.c b/library/psa_crypto.c
index bdb47d2..152fb17 100644
--- a/library/psa_crypto.c
+++ b/library/psa_crypto.c
@@ -1297,8 +1297,8 @@
         return( PSA_ERROR_INVALID_ARGUMENT );
 
     slot = &global_data.key_slots[key];
-    if( slot->type == PSA_KEY_TYPE_NONE )
-        return( PSA_ERROR_EMPTY_SLOT );
+    if( slot->type != PSA_KEY_TYPE_NONE )
+        return( PSA_ERROR_OCCUPIED_SLOT );
 
     if ( lifetime != PSA_KEY_LIFETIME_VOLATILE )
         return( PSA_ERROR_NOT_SUPPORTED );