diff --git a/tests/test-bisect b/tests/test-bisect
--- a/tests/test-bisect
+++ b/tests/test-bisect
@@ -17,7 +17,7 @@ while test $count -lt 32 ; do
     test $count -eq 0 && hg add
     hg ci -m "msg $count" -d "$count 0"
     echo % committed changeset $count
-    count=$(( $count + 1 ))
+    count=`expr $count + 1`
 done
 
 echo % log