diff --git a/src/pack_unpack.c b/src/pack_unpack.c
index abed654..af381a5 100644
--- a/src/pack_unpack.c
+++ b/src/pack_unpack.c
@@ -350,6 +350,7 @@ static int unpack_object(scanner_t *s, json_t *root, va_list *ap)
 {
     int ret = -1;
     int strict = 0;
+    int gotopt = 0;
 
     /* Use a set (emulated by a hashtable) to check that all object
        keys are accessed. Checking that the correct number of keys
@@ -406,7 +407,7 @@ static int unpack_object(scanner_t *s, json_t *root, va_list *ap)
         next_token(s);
 
         if(token(s) == '?') {
-            opt = 1;
+            opt = gotopt = 1;
             next_token(s);
         }
 
@@ -437,10 +438,16 @@ static int unpack_object(scanner_t *s, json_t *root, va_list *ap)
         const char *key;
         json_t *value;
         long unpacked = 0;
-        json_object_foreach(root, key, value) {
-            if(!hashtable_get(&key_set, key)) {
-                unpacked++;
+        if (gotopt) {
+            /* We have optional keys, we need to iter on each key */
+            json_object_foreach(root, key, value) {
+                if(!hashtable_get(&key_set, key)) {
+                    unpacked++;
+                }
             }
+        } else {
+            /* No optional keys, we can just compare the number of items */
+            unpacked = (long)json_object_size(root) - (long)key_set.size;
         }
         if (unpacked) {
             set_error(s, "<validation>", "%li object item(s) left unpacked", unpacked);