diff --git a/mercurial/cmdutil.py b/mercurial/cmdutil.py
--- a/mercurial/cmdutil.py
+++ b/mercurial/cmdutil.py
@@ -2846,10 +2846,6 @@ def revert(ui, repo, ctx, parents, *pats
     mf = ctx.manifest()
     if node == p2:
         parent = p2
-    if node == parent:
-        pmf = mf
-    else:
-        pmf = None
 
     # need all matching names in dirstate and manifest of target rev,
     # so have to walk both. do not print errors if files exist in one
@@ -2964,11 +2960,7 @@ def revert(ui, repo, ctx, parents, *pats
         # in case of merge, files that are actually added can be reported as
         # modified, we need to post process the result
         if p2 != nullid:
-            if pmf is None:
-                # only need parent manifest in the merge case,
-                # so do not read by default
-                pmf = repo[parent].manifest()
-            mergeadd = dsmodified - set(pmf)
+            mergeadd = dsmodified - smf
             dsadded |= mergeadd
             dsmodified -= mergeadd
 
diff --git a/tests/test-revert.t b/tests/test-revert.t
--- a/tests/test-revert.t
+++ b/tests/test-revert.t
@@ -1076,3 +1076,72 @@ check resulting directory against the --
   $ cd ..
   $ diff -U 0 -- content-base-all.txt content-base-explicit.txt | grep _
   [1]
+
+Revert to an ancestor of P2 during a merge (issue5052)
+-----------------------------------------------------
+
+(prepare the repository)
+
+  $ hg init issue5052
+  $ cd issue5052
+  $ echo '.\.orig' > .hgignore
+  $ echo 0 > root
+  $ hg ci -qAm C0
+  $ echo 0 > A
+  $ hg ci -qAm C1
+  $ echo 1 >> A
+  $ hg ci -qm C2
+  $ hg up -q 0
+  $ echo 1 > B
+  $ hg ci -qAm C3
+  $ hg status --rev 'ancestor(.,2)' --rev 2
+  A A
+  $ hg log -G -T '{rev} ({files})\n'
+  @  3 (B)
+  |
+  | o  2 (A)
+  | |
+  | o  1 (A)
+  |/
+  o  0 (.hgignore root)
+  
+
+actual tests: reverting to something else than a merge parent
+
+  $ hg merge
+  1 files updated, 0 files merged, 0 files removed, 0 files unresolved
+  (branch merge, don't forget to commit)
+
+  $ hg status --rev 'p1()'
+  M A
+  $ hg status --rev 'p2()'
+  A B
+  $ hg status --rev '1'
+  M A
+  A B
+  $ hg revert --rev 1 --all
+  reverting A
+  removing B
+  $ hg status --rev 1
+
+From the other parents
+
+  $ hg up -C 'p2()'
+  1 files updated, 0 files merged, 0 files removed, 0 files unresolved
+  $ hg merge
+  1 files updated, 0 files merged, 0 files removed, 0 files unresolved
+  (branch merge, don't forget to commit)
+
+  $ hg status --rev 'p1()'
+  M B
+  $ hg status --rev 'p2()'
+  A A
+  $ hg status --rev '1'
+  M A
+  A B
+  $ hg revert --rev 1 --all
+  reverting A
+  removing B
+  $ hg status --rev 1
+
+  $ cd ..