diff --git a/pyrender/viewer.py b/pyrender/viewer.py
index d2326c3..d0e483f 100644
--- a/pyrender/viewer.py
+++ b/pyrender/viewer.py
@@ -680,7 +680,7 @@ def on_key_press(self, symbol, modifiers):
                 callback = tup
             else:
                 callback = tup[0]
-                if len(tup) == 2:
+                if len(tup) >= 2:
                     args = tup[1]
                 if len(tup) == 3:
                     kwargs = tup[2]