diff --git a/src/backend/postmaster/launch_backend.c b/src/backend/postmaster/launch_backend.c
index d23aed237d2cf..662ac885b9d80 100644
--- a/src/backend/postmaster/launch_backend.c
+++ b/src/backend/postmaster/launch_backend.c
@@ -661,6 +661,15 @@ SubPostmasterMain(int argc, char *argv[])
 	 */
 	LocalProcessControlFile(false);
 
+	/*
+	 * Re-register built-in dynamic managers (e.g. md smgr). On fork-based
+	 * platforms the child inherits the postmaster's already-populated smgr
+	 * table; under EXEC_BACKEND the child starts with an empty table, so we
+	 * must re-run registration. Must happen before shared_preload_libraries
+	 * so extensions can still register their own smgrs from _PG_init().
+	 */
+	register_builtin_dynamic_managers();
+
 	/*
 	 * Reload any libraries that were preloaded by the postmaster.  Since we
 	 * exec'd this process, those libraries didn't come along with us; but we