diff --git a/mercurial/help/config.txt b/mercurial/help/config.txt
--- a/mercurial/help/config.txt
+++ b/mercurial/help/config.txt
@@ -38,6 +38,7 @@ ones.
   - ``<install-root>/etc/mercurial/hgrc.d/*.rc`` (per-installation)
   - ``/etc/mercurial/hgrc`` (per-system)
   - ``/etc/mercurial/hgrc.d/*.rc`` (per-system)
+  - ``<internal>/default.d/*.rc`` (defaults)
 
 .. container:: verbose.windows
 
@@ -51,6 +52,7 @@ ones.
   - ``<install-dir>\Mercurial.ini`` (per-installation)
   - ``<install-dir>\hgrc.d\*.rc`` (per-installation)
   - ``HKEY_LOCAL_MACHINE\SOFTWARE\Mercurial`` (per-installation)
+  - ``<internal>/default.d/*.rc`` (defaults)
 
   .. note::
 
@@ -67,6 +69,7 @@ ones.
   - ``<install-root>/lib/mercurial/hgrc.d/*.rc`` (per-installation)
   - ``/lib/mercurial/hgrc`` (per-system)
   - ``/lib/mercurial/hgrc.d/*.rc`` (per-system)
+  - ``<internal>/default.d/*.rc`` (defaults)
 
 Per-repository configuration options only apply in a
 particular repository. This file is not version-controlled, and
@@ -102,6 +105,13 @@ is running. Options in these files apply
 executed by any user in any directory. Options in these files
 override per-installation options.
 
+Mercurial comes with some default configuration. The default configuration
+files are installed with Mercurial and will be overwritten on upgrades. Default
+configuration files should never be edited by users or administrators but can
+be overridden in other configuration files. So far the directory only contains
+merge tool configuration but packagers can also put other default configuration
+there.
+
 Syntax
 ======
 
diff --git a/mercurial/scmutil.py b/mercurial/scmutil.py
--- a/mercurial/scmutil.py
+++ b/mercurial/scmutil.py
@@ -495,7 +495,13 @@ def walkrepos(path, followsym=False, see
 
 def osrcpath():
     '''return default os-specific hgrc search path'''
-    path = systemrcpath()
+    path = []
+    defaultpath = os.path.join(util.datapath, 'default.d')
+    if os.path.isdir(defaultpath):
+        for f, kind in osutil.listdir(defaultpath):
+            if f.endswith('.rc'):
+                path.append(os.path.join(defaultpath, f))
+    path.extend(systemrcpath())
     path.extend(userrcpath())
     path = [os.path.normpath(f) for f in path]
     return path
diff --git a/setup.py b/setup.py
--- a/setup.py
+++ b/setup.py
@@ -517,6 +517,7 @@ cygwinccompiler.Mingw32CCompiler = Hacke
 
 packagedata = {'mercurial': ['locale/*/LC_MESSAGES/hg.mo',
                              'help/*.txt',
+                             'default.d/*.rc',
                              'dummycert.pem']}
 
 def ordinarypath(p):