diff --git a/migrateSessions.php b/migrateSessions.php
index 90c7c0e..f77d798 100644
--- a/migrateSessions.php
+++ b/migrateSessions.php
@@ -95,7 +95,7 @@
 
 $reasons = ($expired || $noData ? " ($expired expired, $noData no data)" : '');
 if ($test) {
-  printf("Can migrate %d of %d sessions%s. Compressed from %d to %d (%.5f%% savings) in %.5f seconds\n", $migrated, $i, $reasons, $beforeSize, $afterSize, (($beforeSize-$afterSize)/$beforeSize)*100, $elapsedTime);
+  printf("Can migrate %d of %d sessions%s. Compressed from %d to %d (%.5f%% savings) in %.5f seconds\n", $migrated, $i, $reasons, $beforeSize, $afterSize, $beforeSize == 0 ? 0 : (($beforeSize-$afterSize)/$beforeSize)*100, $elapsedTime);
 } else {
   printf("Migrated %d of %d session files in %.5f seconds%s\n", $migrated, $i, $elapsedTime, $reasons);
   Mage::app()->cleanCache(Mage_Core_Model_Config::CACHE_TAG);