--- a/mercurial/localrepo.py	Sun Aug 10 18:01:03 2008 -0500
+++ b/mercurial/localrepo.py	Sun Aug 10 18:01:03 2008 -0500
@@ -708,7 +708,7 @@
             #    \- 2 --- 4        as the merge base
             #
 
-            cr = manifest1.get(cf, nullid)
+            cr = manifest1.get(cf)
             nfp = fp2
 
             if manifest2: # branch merge
@@ -717,6 +717,24 @@
                         cr = manifest2[cf]
                         nfp = fp1
 
+            # find source in nearest ancestor if we've lost track
+            if not cr:
+                self.ui.debug(_(" %s: searching for copy revision for %s\n") %
+                              (fn, cf))
+                p1 = self.dirstate.parents()[0]
+                rev = self.changelog.rev(p1)
+                seen = {-1:None}
+                visit = [rev]
+                while visit:
+                    for p in self.changelog.parentrevs(visit.pop(0)):
+                        if p not in seen:
+                            seen[p] = True
+                            visit.append(p)
+                            ctx = self.changectx(p)
+                            if cf in ctx:
+                                cr = ctx[cf].filenode()
+                                break
+
             self.ui.debug(_(" %s: copy %s:%s\n") % (fn, cf, hex(cr)))
             meta["copy"] = cf
             meta["copyrev"] = hex(cr)

--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/tests/test-issue1175	Sun Aug 10 18:01:03 2008 -0500
@@ -0,0 +1,20 @@
+#!/bin/sh
+rm -rf a
+hg init a
+cd a
+touch a
+hg ci -Am0
+hg mv a a1
+hg ci -m1
+hg co 0
+hg mv a a2
+hg up
+hg ci -m2
+
+touch a
+hg ci -Am3
+hg mv a b
+hg ci -Am4 a
+hg ci --debug --traceback -Am5 b
+hg verify
+hg export --git tip

--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/tests/test-issue1175.out	Sun Aug 10 18:01:03 2008 -0500
@@ -0,0 +1,24 @@
+adding a
+1 files updated, 0 files merged, 1 files removed, 0 files unresolved
+warning: detected divergent renames of a to:
+ a2
+ a1
+1 files updated, 0 files merged, 0 files removed, 0 files unresolved
+adding a
+b
+ b: searching for copy revision for a
+ b: copy a:b80de5d138758541c5f05265ad144ab9fa86d1db
+checking changesets
+checking manifests
+crosschecking files in changesets and manifests
+checking files
+4 files, 6 changesets, 4 total revisions
+# HG changeset patch
+# User test
+# Date 0 0
+# Node ID 755e75751bf67eb4378bca61987df035d90a7a06
+# Parent  7399822c2e395fe7d57c2fcf4b310f6fb22f8c2d
+5
+
+diff --git a/b b/b
+new file mode 100644