diff --git a/electrum/blockchain.py b/electrum/blockchain.py
index f37209504..23bb9e239 100644
--- a/electrum/blockchain.py
+++ b/electrum/blockchain.py
@@ -106,9 +106,9 @@ def PoWHash(x):
     util.print_error("11")
     r = sha512(Hash(x))
     util.print_error("22")
-    r1 = ripemd160(r[:len(r) / 2])
+    r1 = ripemd160(r[:len(r) // 2])
     util.print_error("33")
-    r2 = ripemd160(r[len(r) / 2:])
+    r2 = ripemd160(r[len(r) // 2:])
     util.print_error("44")
     r3 = Hash(r1 + r2)
     util.print_error("55")