diff --git a/rsa/common.py b/rsa/common.py
index e7df21d..b5a966a 100644
--- a/rsa/common.py
+++ b/rsa/common.py
@@ -49,8 +49,8 @@ def bit_size(num: int) -> int:
 
     try:
         return num.bit_length()
-    except AttributeError:
-        raise TypeError('bit_size(num) only supports integers, not %r' % type(num))
+    except AttributeError as ex:
+        raise TypeError('bit_size(num) only supports integers, not %r' % type(num)) from ex
 
 
 def byte_size(number: int) -> int: