diff --git a/build_tools/requirements.txt b/build_tools/requirements.txt
index d652b7e499..a0c7ba392d 100644
--- a/build_tools/requirements.txt
+++ b/build_tools/requirements.txt
@@ -26,7 +26,6 @@ lxml
 pytools 
 cffi
 dominate
-html5lib
 importlib-resources
 bumps
 html2text
diff --git a/src/sas/qtgui/Utilities/TabbedModelEditor.py b/src/sas/qtgui/Utilities/TabbedModelEditor.py
index c7d22b461e..8cce2613b6 100644
--- a/src/sas/qtgui/Utilities/TabbedModelEditor.py
+++ b/src/sas/qtgui/Utilities/TabbedModelEditor.py
@@ -39,6 +39,7 @@ def __init__(self, parent=None, edit_only=False):
         self.edit_only = edit_only
         self.is_modified = False
         self.label = None
+        self.builtinmodels = self.allBuiltinModels()
 
         self.addWidgets()
 
@@ -141,6 +142,15 @@ def onLoad(self):
             self.tabWidget.removeTab(1)
         self.loadFile(filename)
 
+    def allBuiltinModels(self):
+        """
+        create a list of all builtin models
+        """
+        from sas.sascalc.fit.models import ModelManager
+        model_list = ModelManager().cat_model_list()
+        model_names = [model.name for model in model_list]
+        return model_names
+
     def loadFile(self, filename):
         """
         Performs the load operation and updates the view
@@ -444,6 +454,14 @@ def canWriteModel(self, model=None, full_path=""):
                 QtWidgets.QMessageBox.critical(self, "Plugin Error", msg)
                 # Don't accept but return
                 return False
+
+        if model['filename'].casefold() in (model.casefold() for model in self.builtinmodels):
+            # notify the viewer
+            msg = "Built-in model with specified name already exists.\n"
+            msg += "Please specify different filename."
+            QtWidgets.QMessageBox.critical(self, "Plugin Error", msg)
+            # Don't accept but return
+            return False
         # Update model editor if plugin definition changed
         func_str = model['text']
         msg = None