diff --git a/mercurial/configitems.py b/mercurial/configitems.py
--- a/mercurial/configitems.py
+++ b/mercurial/configitems.py
@@ -1084,6 +1084,11 @@
 )
 coreconfigitem(
     b'experimental',
+    b'sharesafe-disallow-outdated-shares',
+    default=False,
+)
+coreconfigitem(
+    b'experimental',
     b'sharesafe-warn-outdated-shares',
     default=True,
 )
diff --git a/mercurial/localrepo.py b/mercurial/localrepo.py
--- a/mercurial/localrepo.py
+++ b/mercurial/localrepo.py
@@ -608,6 +608,15 @@
                     requirements,
                 )
             elif ui.configbool(
+                b'experimental', b'sharesafe-disallow-outdated-shares'
+            ):
+                raise error.Abort(
+                    _(
+                        b'source repository uses share-safe while'
+                        b' current share does not'
+                    )
+                )
+            elif ui.configbool(
                 b'experimental', b'sharesafe-warn-outdated-shares'
             ):
                 ui.warn(
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
@@ -397,6 +397,9 @@
   |
   o  f3ba8b99bb6f897c87bbc1c07b75c6ddf43a4f77: added foo
   
+  $ hg log -GT "{node}: {desc}\n" -R ../nss-share --config experimental.sharesafe-disallow-outdated-shares=true
+  abort: source repository uses share-safe while current share does not
+  [255]
 
   $ hg log -GT "{node}: {desc}\n" -R ../nss-share
   warning: source repository supports share-safe functionality. Reshare to upgrade.