diff --git a/qt/applications/workbench/workbench/plotting/figureinteraction.py b/qt/applications/workbench/workbench/plotting/figureinteraction.py
index f6e474f0f0d9..020dc6f3578a 100644
--- a/qt/applications/workbench/workbench/plotting/figureinteraction.py
+++ b/qt/applications/workbench/workbench/plotting/figureinteraction.py
@@ -861,7 +861,7 @@ def _change_plot_normalization(self, ax):
                         raise RuntimeError("No spectrum number associated with plot of " "workspace '{}'".format(workspace.name()))
 
                 arg_set_copy = copy(arg_set)
-                for key in ["function", "workspaces", "autoscale_on_update", "norm"]:
+                for key in ["function", "workspaces", "autoscale_on_update", "norm", "argType"]:
                     try:
                         del arg_set_copy[key]
                     except KeyError: