diff --git a/Lib/idlelib/AutoIndent.py b/Lib/idlelib/AutoIndent.py
index eff398b..4fbbedf 100644
--- a/Lib/idlelib/AutoIndent.py
+++ b/Lib/idlelib/AutoIndent.py
@@ -462,7 +462,7 @@
             effective = effective + 1
         elif ch == '\t':
             raw = raw + 1
-            effective = (effective / tabwidth + 1) * tabwidth
+            effective = (int(effective / tabwidth) + 1) * tabwidth
         else:
             break
     return raw, effective