diff --git a/mercurial/dispatch.py b/mercurial/dispatch.py
--- a/mercurial/dispatch.py
+++ b/mercurial/dispatch.py
@@ -36,13 +36,16 @@
     help,
     hg,
     hook,
+    localrepo,
     profiling,
     pycompat,
     rcutil,
     registrar,
+    requirements as requirementsmod,
     scmutil,
     ui as uimod,
     util,
+    vfs,
 )
 
 from .utils import (
@@ -939,6 +942,29 @@
     return ret
 
 
+def _readsharedsourceconfig(ui, path):
+    """if the current repository is shared one, this tries to read
+    .hg/hgrc of shared source if we are in share-safe mode
+
+    Config read is loaded into the ui object passed
+
+    This should be called before reading .hg/hgrc or the main repo
+    as that overrides config set in shared source"""
+    try:
+        with open(os.path.join(path, b".hg", b"requires"), "rb") as fp:
+            requirements = set(fp.read().splitlines())
+            if not (
+                requirementsmod.SHARESAFE_REQUIREMENT in requirements
+                and requirementsmod.SHARED_REQUIREMENT in requirements
+            ):
+                return
+            hgvfs = vfs.vfs(os.path.join(path, b".hg"))
+            sharedvfs = localrepo._getsharedvfs(hgvfs, requirements)
+            ui.readconfig(sharedvfs.join(b"hgrc"), path)
+    except IOError:
+        pass
+
+
 def _getlocal(ui, rpath, wd=None):
     """Return (path, local ui object) for the given target path.
 
@@ -959,12 +985,14 @@
     else:
         lui = ui.copy()
         if rcutil.use_repo_hgrc():
+            _readsharedsourceconfig(lui, path)
             lui.readconfig(os.path.join(path, b".hg", b"hgrc"), path)
 
     if rpath:
         path = lui.expandpath(rpath)
         lui = ui.copy()
         if rcutil.use_repo_hgrc():
+            _readsharedsourceconfig(lui, path)
             lui.readconfig(os.path.join(path, b".hg", b"hgrc"), path)
 
     return path, lui
diff --git a/tests/test-share-safe.t b/tests/test-share-safe.t
--- a/tests/test-share-safe.t
+++ b/tests/test-share-safe.t
@@ -102,21 +102,14 @@
   share
   $ hg extdiff -R ../source -p echo
 
-BROKEN: the command below does not work but debugextensions says that extension
+BROKEN: the command below will not work if config of shared source is not loaded
+on dispatch but debugextensions says that extension
 is loaded
   $ hg debugextensions
   extdiff
   share
 
-BROKEN: extdiff command should work here
   $ hg extdiff -p echo
-  hg: unknown command 'extdiff'
-  'extdiff' is provided by the following extension:
-  
-      extdiff       command to allow external programs to compare revisions
-  
-  (use 'hg help extensions' for information on enabling extensions)
-  [255]
 
 However, local .hg/hgrc should override the config set by share source