diff --git a/hgext/remotefilelog/__init__.py b/hgext/remotefilelog/__init__.py
--- a/hgext/remotefilelog/__init__.py
+++ b/hgext/remotefilelog/__init__.py
@@ -487,37 +487,6 @@
         return orig(repo, matcher, added, removed, *args, **kwargs)
     extensions.wrapfunction(scmutil, '_findrenames', findrenames)
 
-    # prefetch files before mergecopies check
-    def computenonoverlap(orig, repo, c1, c2, *args, **kwargs):
-        u1, u2 = orig(repo, c1, c2, *args, **kwargs)
-        if isenabled(repo):
-            m1 = c1.manifest()
-            m2 = c2.manifest()
-            files = []
-
-            sparsematch1 = repo.maybesparsematch(c1.rev())
-            if sparsematch1:
-                sparseu1 = set()
-                for f in u1:
-                    if sparsematch1(f):
-                        files.append((f, hex(m1[f])))
-                        sparseu1.add(f)
-                u1 = sparseu1
-
-            sparsematch2 = repo.maybesparsematch(c2.rev())
-            if sparsematch2:
-                sparseu2 = set()
-                for f in u2:
-                    if sparsematch2(f):
-                        files.append((f, hex(m2[f])))
-                        sparseu2.add(f)
-                u2 = sparseu2
-
-            # batch fetch the needed files from the server
-            repo.fileservice.prefetch(files)
-        return u1, u2
-    extensions.wrapfunction(copies, '_computenonoverlap', computenonoverlap)
-
     # prefetch files before pathcopies check
     def computeforwardmissing(orig, a, b, match=None):
         missing = orig(a, b, match=match)
diff --git a/mercurial/copies.py b/mercurial/copies.py
--- a/mercurial/copies.py
+++ b/mercurial/copies.py
@@ -353,26 +353,6 @@
     return _chain(x, y, _backwardrenames(x, a, match=match),
                   _forwardcopies(a, y, match=match))
 
-def _computenonoverlap(repo, c1, c2, addedinm1, addedinm2, debug=True):
-    """Computes, based on addedinm1 and addedinm2, the files exclusive to c1
-    and c2. This is its own function so extensions can easily wrap this call
-    to see what files mergecopies is about to process.
-
-    Even though c1 and c2 are not used in this function, they are useful in
-    other extensions for being able to read the file nodes of the changed files.
-    """
-    u1 = sorted(addedinm1 - addedinm2)
-    u2 = sorted(addedinm2 - addedinm1)
-
-    if debug:
-        header = "  unmatched files in %s"
-        if u1:
-            repo.ui.debug("%s:\n   %s\n" % (header % 'local', "\n   ".join(u1)))
-        if u2:
-            repo.ui.debug("%s:\n   %s\n" % (header % 'other', "\n   ".join(u2)))
-
-    return u1, u2
-
 def mergecopies(repo, c1, c2, base):
     """
     Finds moves and copies between context c1 and c2 that are relevant for
@@ -555,7 +535,14 @@
     # find interesting file sets from manifests
     addedinm1 = m1.filesnotin(mb, repo.narrowmatch())
     addedinm2 = m2.filesnotin(mb, repo.narrowmatch())
-    u1, u2 = _computenonoverlap(repo, c1, c2, addedinm1, addedinm2)
+    u1 = sorted(addedinm1 - addedinm2)
+    u2 = sorted(addedinm2 - addedinm1)
+
+    header = "  unmatched files in %s"
+    if u1:
+        repo.ui.debug("%s:\n   %s\n" % (header % 'local', "\n   ".join(u1)))
+    if u2:
+        repo.ui.debug("%s:\n   %s\n" % (header % 'other', "\n   ".join(u2)))
 
     fullcopy = copies1.copy()
     fullcopy.update(copies2)
diff --git a/tests/test-remotefilelog-sparse.t b/tests/test-remotefilelog-sparse.t
--- a/tests/test-remotefilelog-sparse.t
+++ b/tests/test-remotefilelog-sparse.t
@@ -98,12 +98,5 @@
   $ clearcache
   $ hg prefetch -r '. + .^' -I x -I z
   4 files fetched over 1 fetches - (4 misses, 0.00% hit ratio) over * (glob)
-Originally this was testing that the rebase doesn't fetch pointless
-blobs. Right now it fails because core's sparse can't load a spec from
-the working directory. Presumably there's a fix, but I'm not sure what it is.
   $ hg rebase -d 2 --keep
   rebasing 1:876b1317060d "x2" (foo)
-  transaction abort!
-  rollback completed
-  abort: cannot parse sparse patterns from working directory
-  [255]