diff --git a/doc/hgrc.5.txt b/doc/hgrc.5.txt
--- a/doc/hgrc.5.txt
+++ b/doc/hgrc.5.txt
@@ -878,6 +878,11 @@ User interface controls.
     be prompted to enter a username. If no username is entered, the
     default ``USER@HOST`` is used instead.
     Default is False.
+``commitsubrepos``
+    Whether to commit modified subrepositories when committing the
+    parent repository. If False and one subrepository has uncommitted
+    changes, abort the commit.
+    Default is True.
 ``debug``
     Print debugging information. True or False. Default is False.
 ``editor``
diff --git a/mercurial/help/subrepos.txt b/mercurial/help/subrepos.txt
--- a/mercurial/help/subrepos.txt
+++ b/mercurial/help/subrepos.txt
@@ -78,7 +78,10 @@ Interaction with Mercurial Commands
 :commit: commit creates a consistent snapshot of the state of the
     entire project and its subrepositories. It does this by first
     attempting to commit all modified subrepositories, then recording
-    their state and finally committing it in the parent repository.
+    their state and finally committing it in the parent
+    repository. Mercurial can be made to abort if any subrepository
+    content is modified by setting "ui.commitsubrepos=no" in a
+    configuration file (see :hg:`help config`).
 
 :diff: diff does not recurse in subrepos unless -S/--subrepos is
     specified. Changes are displayed as usual, on the subrepositories
diff --git a/mercurial/localrepo.py b/mercurial/localrepo.py
--- a/mercurial/localrepo.py
+++ b/mercurial/localrepo.py
@@ -933,6 +933,12 @@ class localrepository(repo.repository):
                 if '.hgsubstate' not in changes[0]:
                     changes[0].insert(0, '.hgsubstate')
 
+            if subs and not self.ui.configbool('ui', 'commitsubrepos', True):
+                changedsubs = [s for s in subs if wctx.sub(s).dirty(True)]
+                if changedsubs:
+                    raise util.Abort(_("uncommitted changes in subrepo %s")
+                                     % changedsubs[0])
+
             # make sure all explicit patterns are matched
             if not force and match.files():
                 matched = set(changes[0] + changes[1] + changes[2])
diff --git a/tests/test-subrepo.t b/tests/test-subrepo.t
--- a/tests/test-subrepo.t
+++ b/tests/test-subrepo.t
@@ -75,16 +75,19 @@ add sub sub
   commit: (clean)
   update: (current)
 
-bump sub rev
+bump sub rev (and check it is ignored by ui.commitsubrepos)
 
   $ echo b > s/a
   $ hg -R s ci -ms1
-  $ hg ci -m3
+  $ hg --config ui.commitsubrepos=no ci -m3
   committing subrepository s
 
-leave sub dirty
+leave sub dirty (and check ui.commitsubrepos=no aborts the commit)
 
   $ echo c > s/a
+  $ hg --config ui.commitsubrepos=no ci -m4
+  abort: uncommitted changes in subrepo s
+  [255]
   $ hg ci -m4
   committing subrepository s
   $ hg tip -R s