diff --git a/Tools/gdb/libpython.py b/Tools/gdb/libpython.py
index 88fb0aa..5c59b99 100755
--- a/Tools/gdb/libpython.py
+++ b/Tools/gdb/libpython.py
@@ -1518,8 +1518,8 @@
             except RuntimeError:
                 return 'PyCFunction invocation (unable to read "func")'
 
-        elif caller in {'_PyCFunction_FastCallDict',
-                        '_PyCFunction_FastCallKeywords'}:
+        elif caller in ('_PyCFunction_FastCallDict',
+                        '_PyCFunction_FastCallKeywords'):
             try:
                 func = older._gdbframe.read_var('func_obj')
                 return str(func)