diff --git a/mercurial/patch.py b/mercurial/patch.py
--- a/mercurial/patch.py
+++ b/mercurial/patch.py
@@ -2273,6 +2273,11 @@ def diff(repo, node1=None, node2=None, m
     modified = sorted(modifiedset)
     added = sorted(addedset)
     removed = sorted(removedset)
+    for dst, src in copy.items():
+        if src not in ctx1:
+            # Files merged in during a merge and then copied/renamed are
+            # reported as copies. We want to show them in the diff as additions.
+            del copy[dst]
 
     def difffn(opts, losedata):
         return trydiff(repo, revs, ctx1, ctx2, modified, added, removed,
diff --git a/tests/test-diffdir.t b/tests/test-diffdir.t
--- a/tests/test-diffdir.t
+++ b/tests/test-diffdir.t
@@ -68,3 +68,10 @@ parent 1, the diff should be relative to
   +++ b/a2
   @@ -0,0 +1,1 @@
   +foo
+  $ hg diff --nodates --git
+  diff --git a/a2 b/a2
+  new file mode 100644
+  --- /dev/null
+  +++ b/a2
+  @@ -0,0 +1,1 @@
+  +foo