diff --git a/hgext/extdiff.py b/hgext/extdiff.py
--- a/hgext/extdiff.py
+++ b/hgext/extdiff.py
@@ -65,6 +65,9 @@ def dodiff(ui, repo, diffcmd, diffopts, 
             ui.write_err(_('making snapshot of %d files from rev %s\n') %
                          (len(files), short(node)))
         for fn in files:
+            if not fn in mf:
+                # skipping new file after a merge ?
+                continue
             wfn = util.pconvert(fn)
             ui.note('  %s\n' % wfn)
             dest = os.path.join(base, wfn)
diff --git a/tests/test-extdiff b/tests/test-extdiff
--- a/tests/test-extdiff
+++ b/tests/test-extdiff
@@ -26,4 +26,13 @@ hg ci -d '0 0' -mtest1
 echo b >> a
 hg ci -d '1 0' -mtest2
 
-hg falabala -r 0:1 || echo "diff-like tools yield a non-zero exit code"
+hg falabala -r 0:1
+
+# test diff during merge
+hg update 0
+echo b >> b
+hg add b
+hg ci -m "new branch" -d '1 0'
+hg update -C 1
+hg merge tip
+hg falabala || echo "diff-like tools yield a non-zero exit code"
diff --git a/tests/test-extdiff.out b/tests/test-extdiff.out
--- a/tests/test-extdiff.out
+++ b/tests/test-extdiff.out
@@ -29,4 +29,11 @@ options:
 making snapshot of 1 files from rev e27a2475d60a
 making snapshot of 1 files from rev 5e49ec8d3f05
 diffing a.e27a2475d60a a.5e49ec8d3f05
+1 files updated, 0 files merged, 0 files removed, 0 files unresolved
+1 files updated, 0 files merged, 1 files removed, 0 files unresolved
+1 files updated, 0 files merged, 0 files removed, 0 files unresolved
+(branch merge, don't forget to commit)
+making snapshot of 1 files from rev 5e49ec8d3f05
+making snapshot of 1 files from working dir
+diffing a.5e49ec8d3f05 a
 diff-like tools yield a non-zero exit code
diff --git a/tests/test-merge1 b/tests/test-merge1
--- a/tests/test-merge1
+++ b/tests/test-merge1
@@ -23,6 +23,8 @@ hg commit -m "commit #2" -d "1000000 0"
 echo This is file b1 > b
 echo %% no merges expected
 env HGMERGE=../merge hg merge 1
+hg diff --nodates
+hg status
 cd ..; /bin/rm -rf t
 
 mkdir t
@@ -44,6 +46,8 @@ echo %% merge should fail
 env HGMERGE=../merge hg merge 1
 echo %% merge of b expected
 env HGMERGE=../merge hg merge -f 1
+hg diff --nodates
+hg status
 cd ..; /bin/rm -rf t
 echo %%
 
@@ -71,6 +75,8 @@ echo %% merge fails
 env HGMERGE=../merge hg merge 2
 echo %% merge expected!
 env HGMERGE=../merge hg merge -f 2
+hg diff --nodates
+hg status
 cd ..; /bin/rm -rf t
 
 mkdir t
@@ -93,4 +99,6 @@ echo %% merge of b should fail
 env HGMERGE=../merge hg merge 2
 echo %% merge of b expected
 env HGMERGE=../merge hg merge -f 2
+hg diff --nodates
+hg status
 cd ..; /bin/rm -rf t
diff --git a/tests/test-merge1.out b/tests/test-merge1.out
--- a/tests/test-merge1.out
+++ b/tests/test-merge1.out
@@ -4,6 +4,12 @@ merging for b
 merging b
 0 files updated, 1 files merged, 0 files removed, 0 files unresolved
 (branch merge, don't forget to commit)
+diff -r d9e5953b9dec b
+--- /dev/null
++++ b/b
+@@ -0,0 +1,1 @@
++This is file b1
+M b
 0 files updated, 0 files merged, 1 files removed, 0 files unresolved
 %% merge should fail
 abort: 'b' already exists in the working dir and differs from remote
@@ -12,6 +18,12 @@ merging for b
 merging b
 0 files updated, 1 files merged, 0 files removed, 0 files unresolved
 (branch merge, don't forget to commit)
+diff -r d9e5953b9dec b
+--- /dev/null
++++ b/b
+@@ -0,0 +1,1 @@
++This is file b2
+M b
 %%
 1 files updated, 0 files merged, 0 files removed, 0 files unresolved
 Contents of b should be "this is file b1"
@@ -23,6 +35,13 @@ merging for b
 merging b
 0 files updated, 1 files merged, 0 files removed, 0 files unresolved
 (branch merge, don't forget to commit)
+diff -r c1dd73cbf59f b
+--- a/b
++++ b/b
+@@ -1,1 +1,1 @@ This is file b1
+-This is file b1
++This is file b22
+M b
 1 files updated, 0 files merged, 0 files removed, 0 files unresolved
 %% merge of b should fail
 abort: outstanding uncommitted changes
@@ -31,3 +50,10 @@ merging for b
 merging b
 0 files updated, 1 files merged, 0 files removed, 0 files unresolved
 (branch merge, don't forget to commit)
+diff -r c1dd73cbf59f b
+--- a/b
++++ b/b
+@@ -1,1 +1,1 @@ This is file b1
+-This is file b1
++This is file b33
+M b