pygost/gost3410.py | 4 +---

diff --git a/pygost/gost3410.py b/pygost/gost3410.py
index 310992f47594afa4d3681e42fccb3fc9e3b5328894502baa28bf94efa8cd4f44..0d9e0e81ed058b81d8e0d59d1192e20d9c57cf0dd30848e44ada97ce3e2eb0b8 100644
--- a/pygost/gost3410.py
+++ b/pygost/gost3410.py
@@ -54,9 +54,7 @@         self.x = x
         self.y = y
         r1 = self.y * self.y % self.p
         r2 = ((self.x * self.x + self.a) * self.x + self.b) % self.p
-        if r2 < 0:
-            r2 += self.p
-        if r1 != r2:
+        if r1 != self._pos(r2):
             raise ValueError("Invalid parameters")
 
     def _pos(self, v):