diff --git a/eopayment/dummy.py b/eopayment/dummy.py
index 0c89169..6464415 100644
--- a/eopayment/dummy.py
+++ b/eopayment/dummy.py
@@ -230,3 +230,9 @@ class Payment(PaymentCommon):
 
     def cancel(self, amount, bank_data, **kwargs):
         return {}
+
+    @classmethod
+    def guess(self, *, method=None, query_string=None, body=None, headers=None, backends=(), **kwargs):
+        qs = parse_qs(force_text(query_string))
+        if set(qs.keys()) >= {'transaction_id', 'signed'}:
+            return qs['transaction_id'][0]
diff --git a/tests/test_misc.py b/tests/test_misc.py
index 6d8c914..f004785 100644
--- a/tests/test_misc.py
+++ b/tests/test_misc.py
@@ -119,6 +119,13 @@ GUESS_TEST_VECTORS = [
         },
         'result': ['sips2', '668930'],
     },
+    {
+        'name': 'dummy',
+        'kwargs': {
+            'query_string': b'transaction_id=123&ok=1&signed=1',
+        },
+        'result': ['dummy', '123'],
+    },
     {
         'name': 'notfound',
         'kwargs': {},