diff --git a/mercurial/filemerge.py b/mercurial/filemerge.py
index 0b73f1353b..0e8a841d10 100644
--- a/mercurial/filemerge.py
+++ b/mercurial/filemerge.py
@@ -247,16 +247,20 @@ def _matcheol(file, back):
                 util.writefile(file, newdata)
 
 
-@internaltool("abort", nomerge)
-def _iabort(repo, mynode, orig, fcd, fco, fca, toolconf, labels=None):
-    if fcd.changectx().isinmemory():
+@internaltool("abort", fullmerge)
+def _iabort(repo, mynode, orig, fcd, *args, **kwargs):
+    if not fcd.changectx().isinmemory():
+        # Support coming soon; it's tricker to do without IMM and has to be
+        # implemented per-command.
+        raise error.Abort(_("--tool :abort only works with in-memory merge"))
+
+    res = _imerge(repo, mynode, orig, fcd, *args, **kwargs)
+    if res:
         raise error.AbortMergeToolError(
             _("hit merge conflicts, and --tool :abort passed")
         )
     else:
-        # Support coming soon; it's tricker to do without IMM and has to be
-        # implemented per-command.
-        raise error.Abort(_("--tool :abort only works with in-memory merge"))
+        return res
 
 
 @internaltool("prompt", nomerge)
diff --git a/tests/test-rebase-inmemory-abort-tool.t b/tests/test-rebase-inmemory-abort-tool.t
index 7793e9dc03..c4703fc37c 100644
--- a/tests/test-rebase-inmemory-abort-tool.t
+++ b/tests/test-rebase-inmemory-abort-tool.t
@@ -1,6 +1,5 @@
 Tests the :abort merge tool
 
-  $ newrepo
   $ enable rebase fbamend morestatus
   $ setconfig morestatus.show=True
   $ setconfig rebase.singletransaction=True
@@ -8,6 +7,7 @@ Tests the :abort merge tool
   $ setconfig rebase.experimental.inmemory.nomergedriver=False
   $ setconfig rebase.experimental.inmemory.newconflictswitching=True
   $ setconfig rebase.experimental.inmemorywarning="rebasing in-memory!"
+  $ newrepo
 
   $ hg debugdrawdag <<'EOS'
   > c
@@ -23,22 +23,26 @@ Tests the :abort merge tool
   $ hg up c
   2 files updated, 0 files merged, 1 files removed, 0 files unresolved
   $ echo "local change" > b
+
+
+Confirm it fails when rebasing a change that conflicts:
   $ hg rebase -r tip -d . --tool :abort
   rebasing in-memory!
   rebasing 3:955ac081fc7c "g" (tip)
+  merging c
   hit merge conflicts, and --tool :abort passed; exiting.
   $ hg st
   M b
   $ cat b
   local change
 
-A rebase without a conflict behaves the same:
+Confirm rebase without a merge behaves the same:
   $ hg rebase -r tip -d .~1 --tool :abort
   rebasing in-memory!
   rebasing 3:955ac081fc7c "g" (tip)
   saved backup bundle to $TESTTMP/repo1/.hg/strip-backup/955ac081fc7c-77e57574-rebase.hg
 
-It fails without IMM:
+Confirm the flag fails without IMM:
 
   $ setconfig rebase.experimental.inmemory=False
   $ hg up -C .
@@ -46,7 +50,35 @@ It fails without IMM:
   $ hg st
   $ hg rebase -r tip -d . --tool :abort
   rebasing 3:20b9638feb86 "g" (tip)
+  merging c
   transaction abort!
   rollback completed
   abort: --tool :abort only works with in-memory merge
   [255]
+
+Confirm that it rebases a three-way merge, but no conflict:
+  $ newrepo
+  $ $TESTDIR/seq.py 1 5 > a
+  $ hg commit -Aq -m "base"
+  $ $TESTDIR/seq.py 1 10 > a
+  $ hg commit -q -m "extend to 10"
+  $ hg up -q .~1
+  $ $TESTDIR/seq.py 0 5 > a
+  $ hg commit -q -m "prepend with 0"
+  $ hg log -G -r 0:: -T '{rev} {desc}'
+  @  2 prepend with 0
+  |
+  | o  1 extend to 10
+  |/
+  o  0 base
+  
+  $ hg up -qC 0
+  $ hg rebase -r 1 -d 2 --tool :abort
+  rebasing in-memory!
+  rebasing 1:12cba56c6d27 "extend to 10"
+  merging a
+  saved backup bundle to $TESTTMP/repo2/.hg/strip-backup/12cba56c6d27-14ff6d99-rebase.hg
+  $ hg cat -r tip a | wc -l | xargs
+  11
+
+^ (xargs is used for trimming)