diff --git a/src/Gui/Control.cpp b/src/Gui/Control.cpp
index 522c4c21ba..11ca885cd4 100644
--- a/src/Gui/Control.cpp
+++ b/src/Gui/Control.cpp
@@ -109,6 +109,14 @@ void ControlSingleton::showDialog(Gui::TaskView::TaskDialog *dlg)
         }
         return;
     }
+
+    // Since the caller sets up a modeless task panel, it indicates intension
+    // for prolonged editing. So disable auto transaction in the current call
+    // stack.
+    // Do this before showing the dialog because its open() function is called
+    // which may open a transaction but fails when auto transaction is still active.
+    App::AutoTransaction::setEnable(false);
+
     Gui::DockWnd::ComboView* pcComboView = qobject_cast<Gui::DockWnd::ComboView*>
         (Gui::DockWindowManager::instance()->getDockWindow("Combo View"));
     // should return the pointer to combo view
@@ -148,11 +156,6 @@ void ControlSingleton::showDialog(Gui::TaskView::TaskDialog *dlg)
             dw->raise();
         }
     }
-
-    // Since the caller sets up a modeless task panel, it indicates intension
-    // for prolonged editing. So disable auto transaction in the current call
-    // stack.
-    App::AutoTransaction::setEnable(false);
 }
 
 QTabWidget* ControlSingleton::tabPanel() const