diff --git a/tailbone/static/js/tailbone.timesheet.edit.js b/tailbone/static/js/tailbone.timesheet.edit.js
index 75275d52..47473671 100644
--- a/tailbone/static/js/tailbone.timesheet.edit.js
+++ b/tailbone/static/js/tailbone.timesheet.edit.js
@@ -146,12 +146,24 @@ function update_row_hours(row) {
 function cleanup_editor_input() {
     // TODO: is this hacky? invoking timepicker to format the time values
     // in all cases, to avoid "invalid format" from user input
+    var backward = false;
     $('#day-editor .shifts .shift').each(function() {
         var start_time = $(this).children('input[name|="edit_start_time"]');
         var end_time = $(this).children('input[name|="edit_end_time"]');
         $.timepicker._setTime(start_time.data('timepicker'), start_time.val() || '??');
         $.timepicker._setTime(end_time.data('timepicker'), end_time.val() || '??');
+        var t_start = parseTime(start_time.val());
+        var t_end = parseTime(end_time.val());
+        if (t_start && t_end) {
+            if ((t_start.hh > t_end.hh) || ((t_start.hh == t_end.hh) && (t_start.mm > t_end.mm))) {
+                alert("Start time falls *after* end time!  Please fix...");
+                start_time.focus().select();
+                backward = true;
+                return false;
+            }
+        }
     });
+    return !backward;
 }
 
 
diff --git a/tailbone/templates/shifts/timesheet_edit.mako b/tailbone/templates/shifts/timesheet_edit.mako
index bf3036a4..66232391 100644
--- a/tailbone/templates/shifts/timesheet_edit.mako
+++ b/tailbone/templates/shifts/timesheet_edit.mako
@@ -37,10 +37,11 @@
                     {
                         text: "Save Changes",
                         click: function(event) {
-                            $(event.target).button('disable').button('option', 'label', "Saving...");
-                            cleanup_editor_input();
-                            update_timetable();
-                            $('#timetable-form').submit();
+                            if (cleanup_editor_input()) {
+                                $(event.target).button('disable').button('option', 'label', "Saving...");
+                                update_timetable();
+                                $('#timetable-form').submit();
+                            }
                         }
                     },
                     {