diff --git a/mercurial/cmdutil.py b/mercurial/cmdutil.py
--- a/mercurial/cmdutil.py
+++ b/mercurial/cmdutil.py
@@ -628,6 +628,9 @@ def tryimportone(ui, repo, hunk, parents
                     p2 = repo[nullid]
             except error.RepoError:
                 p1, p2 = parents
+            if p2.node() == nullid:
+                ui.warn(_("warning: import the patch as a normal revision\n"
+                          "(use --exact to import the patch as a merge)\n"))
         else:
             p1, p2 = parents
 
diff --git a/tests/test-import-merge.t b/tests/test-import-merge.t
--- a/tests/test-import-merge.t
+++ b/tests/test-import-merge.t
@@ -66,6 +66,8 @@ Test without --exact and diff.p1 != work
   1 files updated, 0 files merged, 0 files removed, 0 files unresolved
   $ hg import ../merge.diff
   applying ../merge.diff
+  warning: import the patch as a normal revision
+  (use --exact to import the patch as a merge)
   $ tipparents
   2:890ecaa90481 addc
   $ hg strip --no-backup tip
@@ -99,6 +101,8 @@ Test with --bypass and diff.p1 != workin
   1 files updated, 0 files merged, 0 files removed, 0 files unresolved
   $ hg import --bypass ../merge.diff
   applying ../merge.diff
+  warning: import the patch as a normal revision
+  (use --exact to import the patch as a merge)
   $ tipparents
   2:890ecaa90481 addc
   $ hg strip --no-backup tip