diff --git a/mercurial/pure/base85.py b/mercurial/pure/base85.py
--- a/mercurial/pure/base85.py
+++ b/mercurial/pure/base85.py
@@ -54,9 +54,10 @@ def b85decode(text):
             try:
                 acc = acc * 85 + _b85dec[c]
             except KeyError:
-                raise TypeError('Bad base85 character at byte %d' % (i + j))
+                raise ValueError('bad base85 character at position %d'
+                                 % (i + j))
         if acc > 4294967295:
-            raise OverflowError('Base85 overflow in hunk starting at byte %d' % i)
+            raise ValueError('Base85 overflow in hunk starting at byte %d' % i)
         out.append(acc)
 
     # Pad final chunk if necessary
diff --git a/tests/test-check-code-hg.t b/tests/test-check-code-hg.t
--- a/tests/test-check-code-hg.t
+++ b/tests/test-check-code-hg.t
@@ -496,9 +496,6 @@
   mercurial/patch.py:0:
    >     except:
    warning: naked except clause
-  mercurial/pure/base85.py:0:
-   >             raise OverflowError('Base85 overflow in hunk starting at byte %d' % i)
-   warning: line over 80 characters
   mercurial/pure/mpatch.py:0:
    >         frags.extend(reversed(new))                    # what was left at the end
    warning: line over 80 characters