diff --git a/hgext/sqlitestore.py b/hgext/sqlitestore.py
--- a/hgext/sqlitestore.py
+++ b/hgext/sqlitestore.py
@@ -76,6 +76,7 @@
 )
 from mercurial.utils import (
     interfaceutil,
+    procutil,
     storageutil,
 )
 
@@ -1005,17 +1006,18 @@
 
     @property
     def _dbconn(self):
-        # SQLite connections can only be used on the thread that created
-        # them. In most cases, this "just works." However, hgweb uses
-        # multiple threads.
-        tid = threading.current_thread().ident
+        # SQLite connections can only be used on the OS and Python thread that
+        # created them. In most cases, this "just works." However, hgweb uses
+        # multiple Python threads. And Mercurial may fork. So we need to check
+        # global state before returning an existing connection.
+        key = (procutil.getpid(), threading.current_thread().ident)
 
         if self._db:
-            if self._db[0] == tid:
+            if self._db[0] == key:
                 return self._db[1]
 
         db = makedb(self.svfs.join('db.sqlite'))
-        self._db = (tid, db)
+        self._db = (key, db)
 
         return db