diff --git a/web/includes/functions.php b/web/includes/functions.php
index ed9850ca3..9a8264548 100644
--- a/web/includes/functions.php
+++ b/web/includes/functions.php
@@ -1676,7 +1676,11 @@ function getDiskPercent()
         Error("disk_total_space returned false for " . ZM_DIR_EVENTS );
         return 0;
     }
-    $space = round(($total - disk_free_space(ZM_DIR_EVENTS)) / $total * 100);
+    $free = disk_free_space(ZM_DIR_EVENTS);
+    if ( ! $free ) {
+        Error("disk_free_space returned false for " . ZM_DIR_EVENTS );
+    }
+    $space = round(($total - $free) / $total * 100);
     return( $space );
 }