diff --git a/upsetplot/plotting.py b/upsetplot/plotting.py
index c69636b..a848a88 100644
--- a/upsetplot/plotting.py
+++ b/upsetplot/plotting.py
@@ -792,10 +792,10 @@ def plot_matrix(self, ax):
                 }
             )
         )
-        styles["linewidth"].fillna(1, inplace=True)
-        styles["facecolor"].fillna(self._facecolor, inplace=True)
-        styles["edgecolor"].fillna(styles["facecolor"], inplace=True)
-        styles["linestyle"].fillna("solid", inplace=True)
+        styles["linewidth"]=styles["linewidth"].fillna(1)
+        styles["facecolor"]=styles["facecolor"].fillna(self._facecolor)
+        styles["edgecolor"]=styles["edgecolor"].fillna(styles["facecolor"])
+        styles["linestyle"]=styles["linestyle"].fillna("solid")
         del styles["hatch"]  # not supported in matrix (currently)
 
         x = np.repeat(np.arange(len(data)), n_cats)