diff --git a/plugins/3MFReader/ThreeMFWorkspaceReader.py b/plugins/3MFReader/ThreeMFWorkspaceReader.py
index 3d4812a677..0377ce7655 100755
--- a/plugins/3MFReader/ThreeMFWorkspaceReader.py
+++ b/plugins/3MFReader/ThreeMFWorkspaceReader.py
@@ -674,51 +674,61 @@ class ThreeMFWorkspaceReader(WorkspaceReader):
                 self._container_registry.removeContainer(container.getId())
             return
 
+        #
+        # Use the number of extruders from the global stack instead of the number of extruder stacks this project file
+        # contains. The Custom FDM Printer can have multiple extruders, but the actual number of extruders in used is
+        # defined in the global stack.
+        # Because for single-extrusion machines, there won't be an extruder stack, so relying on the the extruder count
+        # in the global stack can avoid problems in those cases.
+        #
+        extruder_count_from_global_stack = global_stack.getProperty("machine_extruder_count", "value")
+
         # --
         # load extruder stack files
-        try:
-            for extruder_stack_file in extruder_stack_files:
-                container_id = self._stripFileToId(extruder_stack_file)
-                extruder_file_content = archive.open(extruder_stack_file, "r").read().decode("utf-8")
+        if extruder_count_from_global_stack > 1:
+            try:
+                for extruder_stack_file in extruder_stack_files:
+                    container_id = self._stripFileToId(extruder_stack_file)
+                    extruder_file_content = archive.open(extruder_stack_file, "r").read().decode("utf-8")
 
-                if self._resolve_strategies["machine"] == "override":
-                    # deserialize new extruder stack over the current ones
-                    stack = self._overrideExtruderStack(global_stack, extruder_file_content)
+                    if self._resolve_strategies["machine"] == "override":
+                        # deserialize new extruder stack over the current ones
+                        stack = self._overrideExtruderStack(global_stack, extruder_file_content)
 
-                elif self._resolve_strategies["machine"] == "new":
-                    new_id = extruder_stack_id_map[container_id]
-                    stack = ExtruderStack(new_id)
+                    elif self._resolve_strategies["machine"] == "new":
+                        new_id = extruder_stack_id_map[container_id]
+                        stack = ExtruderStack(new_id)
 
-                    # HACK: the global stack can have a new name, so we need to make sure that this extruder stack
-                    #       references to the new name instead of the old one. Normally, this can be done after
-                    #       deserialize() by setting the metadata, but in the case of ExtruderStack, deserialize()
-                    #       also does addExtruder() to its machine stack, so we have to make sure that it's pointing
-                    #       to the right machine BEFORE deserialization.
-                    extruder_config = configparser.ConfigParser()
-                    extruder_config.read_string(extruder_file_content)
-                    extruder_config.set("metadata", "machine", global_stack_id_new)
-                    tmp_string_io = io.StringIO()
-                    extruder_config.write(tmp_string_io)
-                    extruder_file_content = tmp_string_io.getvalue()
+                        # HACK: the global stack can have a new name, so we need to make sure that this extruder stack
+                        #       references to the new name instead of the old one. Normally, this can be done after
+                        #       deserialize() by setting the metadata, but in the case of ExtruderStack, deserialize()
+                        #       also does addExtruder() to its machine stack, so we have to make sure that it's pointing
+                        #       to the right machine BEFORE deserialization.
+                        extruder_config = configparser.ConfigParser()
+                        extruder_config.read_string(extruder_file_content)
+                        extruder_config.set("metadata", "machine", global_stack_id_new)
+                        tmp_string_io = io.StringIO()
+                        extruder_config.write(tmp_string_io)
+                        extruder_file_content = tmp_string_io.getvalue()
 
-                    stack.deserialize(extruder_file_content)
+                        stack.deserialize(extruder_file_content)
 
-                    # Ensure a unique ID and name
-                    stack._id = new_id
+                        # Ensure a unique ID and name
+                        stack._id = new_id
 
-                    self._container_registry.addContainer(stack)
-                    extruder_stacks_added.append(stack)
-                    containers_added.append(stack)
-                else:
-                    Logger.log("w", "Unknown resolve strategy: %s", self._resolve_strategies["machine"])
+                        self._container_registry.addContainer(stack)
+                        extruder_stacks_added.append(stack)
+                        containers_added.append(stack)
+                    else:
+                        Logger.log("w", "Unknown resolve strategy: %s", self._resolve_strategies["machine"])
 
-                extruder_stacks.append(stack)
-        except:
-            Logger.logException("w", "We failed to serialize the stack. Trying to clean up.")
-            # Something went really wrong. Try to remove any data that we added. 
-            for container in containers_added:
-                self._container_registry.removeContainer(container.getId())
-            return
+                    extruder_stacks.append(stack)
+            except:
+                Logger.logException("w", "We failed to serialize the stack. Trying to clean up.")
+                # Something went really wrong. Try to remove any data that we added.
+                for container in containers_added:
+                    self._container_registry.removeContainer(container.getId())
+                return
 
         #
         # Replacing the old containers if resolve is "new".
@@ -823,9 +833,6 @@ class ThreeMFWorkspaceReader(WorkspaceReader):
         if extruder_stacks:
             for stack in extruder_stacks:
                 ExtruderManager.getInstance().registerExtruder(stack, global_stack.getId())
-        else:
-            # Machine has no extruders, but it needs to be registered with the extruder manager.
-            ExtruderManager.getInstance().registerExtruder(None, global_stack.getId())
 
         Logger.log("d", "Workspace loading is notifying rest of the code of changes...")