diff --git a/src/gcal-edit-dialog.c b/src/gcal-edit-dialog.c
index 34dd1e78..46d6d3f3 100644
--- a/src/gcal-edit-dialog.c
+++ b/src/gcal-edit-dialog.c
@@ -300,10 +300,12 @@ sync_datetimes (GcalEditDialog *self,
 {
   GDateTime *start, *end, *new_date;
   GtkWidget *date_widget, *time_widget;
-  gboolean is_start;
+  gboolean is_start_time, is_start_date;
   gint hour_to_add;
 
-  is_start = (widget == self->start_time_selector || widget == self->start_date_selector);
+  is_start_time = (widget == self->start_time_selector);
+  is_start_date = (widget == self->start_date_selector);
+
   start = gcal_edit_dialog_get_date_start (self);
   end = gcal_edit_dialog_get_date_end (self);
 
@@ -317,9 +319,36 @@ sync_datetimes (GcalEditDialog *self,
    */
   hour_to_add = gtk_toggle_button_get_active (GTK_TOGGLE_BUTTON (self->all_day_check)) ? 0 : 1;
 
-  if (is_start)
+  if (is_start_date)
     {
-      new_date = g_date_time_add_hours (start, hour_to_add);
+      if (hour_to_add)
+        {
+          if (g_date_time_difference(end, start) < 0)
+            {
+              new_date = g_date_time_add_hours (start, hour_to_add + 24);
+
+              date_widget = self->end_date_selector;
+              time_widget = self->end_time_selector;
+            }
+          else
+            {
+              new_date = g_date_time_add_hours (start, hour_to_add);
+
+              date_widget = self->end_date_selector;
+              time_widget = self->end_time_selector;
+            }
+        }
+      else
+        {
+          new_date = g_date_time_add_hours (start, hour_to_add);
+
+          date_widget = self->end_date_selector;
+          time_widget = self->end_time_selector;
+        }
+    }
+  else if (is_start_time)
+    {
+      new_date = g_date_time_add_hours (start, hour_to_add + 24);
 
       date_widget = self->end_date_selector;
       time_widget = self->end_time_selector;