diff -r 6def44ab4769 -r 09d0022cad83 mercurial/graphmod.py
--- a/mercurial/graphmod.py	Fri May 06 19:24:25 2016 +0000
+++ b/mercurial/graphmod.py	Mon May 16 16:41:26 2016 +0100
@@ -668,8 +668,8 @@
             return -num <= i if num < 0 else (len(lines) - i) <= num
         for i, line in enumerate(lines):
             line[:] = [c[-1] if _drawgp(c, i) else parent for c in line]
-        edgemap = dict(
-            (e, c if len(c) < 2 else parent) for e, c in edgemap.items())
+        edgemap.update(
+            (e, (c if len(c) < 2 else parent)) for e, c in edgemap.items())
 
     # print lines
     indentation_level = max(ncols, ncols + coldiff)