diff --git a/src/Mod/Path/PathScripts/PathSimulatorGui.py b/src/Mod/Path/PathScripts/PathSimulatorGui.py
index 8d60e472fd..6e9a16b527 100644
--- a/src/Mod/Path/PathScripts/PathSimulatorGui.py
+++ b/src/Mod/Path/PathScripts/PathSimulatorGui.py
@@ -480,22 +480,30 @@ class PathSimulation:
         self.cutTool.ViewObject.hide()
         self.iprogress = 0
         self.EndSimulation()
+        
+    def InvalidOperation(self):
+        if len(self.activeOps) == 0:
+          return True
+        if (self.tool == None):
+          TSError("No tool assigned for the operation")
+          return True
+        return false
 
     def SimFF(self):
-        if len(self.activeOps) == 0:
+        if self.InvalidOperation():
             return
         self.GuiBusy(True)
         self.timer.start(1)
         self.disableAnim = True
 
     def SimStep(self):
-        if len(self.activeOps) == 0:
+        if self.InvalidOperation():
             return
         self.disableAnim = False
         self.PerformCut()
 
     def SimPlay(self):
-        if len(self.activeOps) == 0:
+        if self.InvalidOperation():
             return
         self.disableAnim = False
         self.GuiBusy(True)
diff --git a/src/Mod/Path/PathSimulator/App/PathSim.cpp b/src/Mod/Path/PathSimulator/App/PathSim.cpp
index bc3e2b7ef5..2901c13d3a 100644
--- a/src/Mod/Path/PathSimulator/App/PathSim.cpp
+++ b/src/Mod/Path/PathSimulator/App/PathSim.cpp
@@ -125,21 +125,24 @@ Base::Placement * PathSim::ApplyCommand(Base::Placement * pos, Command * cmd)
 	Point3D fromPos(*pos);
 	Point3D toPos(*pos);
 	toPos.UpdateCmd(*cmd);
-	if (cmd->Name == "G0" || cmd->Name == "G1")
+	if (m_tool != NULL)
 	{
-        m_stock->ApplyLinearTool(fromPos, toPos, *m_tool);
-	}
-	else if (cmd->Name == "G2")
-	{
-		Vector3d vcent = cmd->getCenter();
-		Point3D cent(vcent);
-		m_stock->ApplyCircularTool(fromPos, toPos, cent, *m_tool, false);
-	}
-	else if (cmd->Name == "G3")
-	{
-		Vector3d vcent = cmd->getCenter();
-		Point3D cent(vcent);
-		m_stock->ApplyCircularTool(fromPos, toPos, cent, *m_tool, true);
+		if (cmd->Name == "G0" || cmd->Name == "G1")
+		{
+			m_stock->ApplyLinearTool(fromPos, toPos, *m_tool);
+		}
+		else if (cmd->Name == "G2")
+		{
+			Vector3d vcent = cmd->getCenter();
+			Point3D cent(vcent);
+			m_stock->ApplyCircularTool(fromPos, toPos, cent, *m_tool, false);
+		}
+		else if (cmd->Name == "G3")
+		{
+			Vector3d vcent = cmd->getCenter();
+			Point3D cent(vcent);
+			m_stock->ApplyCircularTool(fromPos, toPos, cent, *m_tool, true);
+		}
 	}
 
 	Base::Placement *plc = new Base::Placement();