diff --git a/plugins/CuraEngineBackend/StartSliceJob.py b/plugins/CuraEngineBackend/StartSliceJob.py
index 78dd4eafd2..12d95b94bc 100644
--- a/plugins/CuraEngineBackend/StartSliceJob.py
+++ b/plugins/CuraEngineBackend/StartSliceJob.py
@@ -45,35 +45,31 @@ class GcodeStartEndFormatter(Formatter):
         # The kwargs dictionary contains a dictionary for each stack (with a string of the extruder_nr as their key),
         # and a default_extruder_nr to use when no extruder_nr is specified
 
-        if isinstance(key, str):
+        try:
+            extruder_nr = int(kwargs["default_extruder_nr"])
+        except ValueError:
+            extruder_nr = -1
+
+        key_fragments = [fragment.strip() for fragment in key.split(",")]
+        if len(key_fragments) == 2:
             try:
-                extruder_nr = int(kwargs["default_extruder_nr"])
+                extruder_nr = int(key_fragments[1])
             except ValueError:
-                extruder_nr = -1
-
-            key_fragments = [fragment.strip() for fragment in key.split(",")]
-            if len(key_fragments) == 2:
                 try:
-                    extruder_nr = int(key_fragments[1])
-                except ValueError:
-                    try:
-                        extruder_nr = int(kwargs["-1"][key_fragments[1]]) # get extruder_nr values from the global stack
-                    except (KeyError, ValueError):
-                        # either the key does not exist, or the value is not an int
-                        Logger.log("w", "Unable to determine stack nr '%s' for key '%s' in start/end g-code, using global stack", key_fragments[1], key_fragments[0])
-            elif len(key_fragments) != 1:
-                Logger.log("w", "Incorrectly formatted placeholder '%s' in start/end g-code", key)
-                return "{" + str(key) + "}"
-
-            key = key_fragments[0]
-            try:
-                return kwargs[str(extruder_nr)][key]
-            except KeyError:
-                Logger.log("w", "Unable to replace '%s' placeholder in start/end g-code", key)
-                return "{" + key + "}"
-        else:
+                    extruder_nr = int(kwargs["-1"][key_fragments[1]]) # get extruder_nr values from the global stack
+                except (KeyError, ValueError):
+                    # either the key does not exist, or the value is not an int
+                    Logger.log("w", "Unable to determine stack nr '%s' for key '%s' in start/end g-code, using global stack", key_fragments[1], key_fragments[0])
+        elif len(key_fragments) != 1:
             Logger.log("w", "Incorrectly formatted placeholder '%s' in start/end g-code", key)
-            return "{" + str(key) + "}"
+            return "{" + key + "}"
+
+        key = key_fragments[0]
+        try:
+            return kwargs[str(extruder_nr)][key]
+        except KeyError:
+            Logger.log("w", "Unable to replace '%s' placeholder in start/end g-code", key)
+            return "{" + key + "}"
 
 
 ##  Job class that builds up the message of scene data to send to CuraEngine.