diff --git a/irc.py b/irc.py
index 0f5ecf8..397b3f1 100644
--- a/irc.py
+++ b/irc.py
@@ -385,7 +385,9 @@ class PesterHandler(DefaultCommandHandler):
             modes = list(self.parent.mainwindow.modes)
             if modes and modes[0] == "+": modes = modes[1:]
             if mode[0] == "+":
-                modes.extend(mode[1:])
+                for m in mode[1:]:
+                    if m not in modes:
+                        modes.extend(m)
             elif mode[0] == "-":
                 for i in mode[1:]:
                     try:
diff --git a/memos.py b/memos.py
index d14453a..6818826 100644
--- a/memos.py
+++ b/memos.py
@@ -616,7 +616,9 @@ class PesterMemo(PesterConvo):
         if chanmodes and chanmodes[0] == "+": chanmodes = chanmodes[1:]
         modes = str(modes)
         if modes[0] == "+":
-            chanmodes.extend(modes[1:])
+            for m in modes[1:]:
+                if m not in chanmodes:
+                    chanmodes.extend(m)
             if modes.find("s") >= 0: self.chanHide.setChecked(True)
             if modes.find("i") >= 0: self.chanInvite.setChecked(True)
             if modes.find("m") >= 0: self.chanMod.setChecked(True)