diff --git a/deploy/drhider/drhider.py b/deploy/drhider/drhider.py
index 919f4ef..1ecf74f 100644
--- a/deploy/drhider/drhider.py
+++ b/deploy/drhider/drhider.py
@@ -80,12 +80,15 @@ def _checksum_inn10(inn: str) -> str:
 
 
 def _checksum_inn12(inn: str) -> str:
-    """Контрольные суммы для 12-значного ИНН."""
+    """Контрольные суммы для 12-значного ИНН (первые 10 цифр)."""
     c1 = [7, 2, 4, 10, 3, 5, 9, 4, 6, 8]
     c2 = [3, 7, 2, 4, 10, 3, 5, 9, 4, 6, 8]
     s1 = sum(int(inn[i]) * c1[i] for i in range(10))
-    s2 = sum(int(inn[i]) * c2[i] for i in range(11))
-    return str((s1 % 11) % 10) + str((s2 % 11) % 10)
+    n1 = (s1 % 11) % 10
+    inn2 = inn + str(n1)
+    s2 = sum(int(inn2[i]) * c2[i] for i in range(11))
+    n2 = (s2 % 11) % 10
+    return str(n1) + str(n2)
 
 
 def _checksum_ogrn(ogrn: str) -> str:
diff --git a/site/services/drhider.py b/site/services/drhider.py
index 5723553..7ebea53 100644
--- a/site/services/drhider.py
+++ b/site/services/drhider.py
@@ -80,12 +80,15 @@ def _checksum_inn10(inn: str) -> str:
 
 
 def _checksum_inn12(inn: str) -> str:
-    """Контрольные суммы для 12-значного ИНН."""
+    """Контрольные суммы для 12-значного ИНН (первые 10 цифр)."""
     c1 = [7, 2, 4, 10, 3, 5, 9, 4, 6, 8]
     c2 = [3, 7, 2, 4, 10, 3, 5, 9, 4, 6, 8]
     s1 = sum(int(inn[i]) * c1[i] for i in range(10))
-    s2 = sum(int(inn[i]) * c2[i] for i in range(11))
-    return str((s1 % 11) % 10) + str((s2 % 11) % 10)
+    n1 = (s1 % 11) % 10
+    inn2 = inn + str(n1)
+    s2 = sum(int(inn2[i]) * c2[i] for i in range(11))
+    n2 = (s2 % 11) % 10
+    return str(n1) + str(n2)
 
 
 def _checksum_ogrn(ogrn: str) -> str: