diff --git a/zoopt/algos/opt_algorithms/racos/sracos.py b/zoopt/algos/opt_algorithms/racos/sracos.py
index 88df0e3..863a6ab 100755
--- a/zoopt/algos/opt_algorithms/racos/sracos.py
+++ b/zoopt/algos/opt_algorithms/racos/sracos.py
@@ -143,7 +143,7 @@ def binary_search(self, iset, x, begin, end):
             return end + 1
         if end == begin + 1:
             return end
-        mid = (begin + end) // 2
+        mid = begin + (end - begin) // 2
         if x_value <= iset[mid].get_value():
             return self.binary_search(iset, x, begin, mid)
         else:
@@ -369,7 +369,7 @@ def binary_search(self, iset, x, begin, end):
             return end + 1
         if end == begin + 1:
             return end
-        mid = (begin + end) // 2
+        mid = begin + (end - begin) // 2
         if x_value <= iset[mid].get_value():
             return self.binary_search(iset, x, begin, mid)
         else: