diff --git a/mercurial/merge.py b/mercurial/merge.py
--- a/mercurial/merge.py
+++ b/mercurial/merge.py
@@ -753,7 +753,7 @@
 
     # check case-folding collision in provisional merged manifest
     foldmap = {}
-    for f in sorted(pmmf):
+    for f in pmmf:
         fold = util.normcase(f)
         if fold in foldmap:
             raise error.Abort(_("case-folding collision between %s and %s")
@@ -762,7 +762,7 @@
 
     # check case-folding of directories
     foldprefix = unfoldprefix = lastfull = ''
-    for fold, f in sorted(foldmap.items()):
+    for fold, f in foldmap.items():
         if fold.startswith(foldprefix) and not f.startswith(unfoldprefix):
             # the folded prefix matches but actual casing is different
             raise error.Abort(_("case-folding collision between "