diff --git a/Documentation/config/core.txt b/Documentation/config/core.txt
index 4f6e519bc0..0210f330d7 100644
--- a/Documentation/config/core.txt
+++ b/Documentation/config/core.txt
@@ -71,7 +71,7 @@ git by avoiding unnecessary scanning of files that have not changed.
 +
 See the "fsmonitor-watchman" section of linkgit:githooks[5].
 +
-Note: The value of this config setting is ignored if the
+Note: The value of this config setting is ignored if the (experimental)
 built-in file system monitor is enabled (see `core.useBuiltinFSMonitor`).
 
 core.fsmonitorHookVersion::
@@ -91,7 +91,7 @@ Note: The value of this config setting is ignored if the
 built-in file system monitor is enabled (see `core.useBuiltinFSMonitor`).
 
 core.useBuiltinFSMonitor::
-	If set to true, enable the built-in file system monitor
+	(EXPERIMENTAL) If set to true, enable the built-in file system monitor
 	daemon for this working directory (linkgit:git-fsmonitor--daemon[1]).
 +
 Like hook-based file system monitors, the built-in file system monitor
diff --git a/Documentation/git-fsmonitor--daemon.txt b/Documentation/git-fsmonitor--daemon.txt
index 154e7684da..cf1d4556a5 100644
--- a/Documentation/git-fsmonitor--daemon.txt
+++ b/Documentation/git-fsmonitor--daemon.txt
@@ -3,7 +3,7 @@ git-fsmonitor--daemon(1)
 
 NAME
 ----
-git-fsmonitor--daemon - A Built-in File System Monitor
+git-fsmonitor--daemon - (EXPERIMENTAL) A Built-in File System Monitor
 
 SYNOPSIS
 --------
@@ -16,6 +16,9 @@ SYNOPSIS
 DESCRIPTION
 -----------
 
+NOTE! This command is still only an experiment, subject to change dramatically
+(or even to be abandoned).
+
 A daemon to watch the working directory for file and directory
 changes using platform-specific file system notification facilities.
 
diff --git a/repo-settings.c b/repo-settings.c
index 935a4f3915..c3671e10e6 100644
--- a/repo-settings.c
+++ b/repo-settings.c
@@ -2,7 +2,8 @@
 #include "config.h"
 #include "repository.h"
 #include "midx.h"
-#include "compat/fsmonitor/fsm-listen.h"
+#include "fsmonitor-ipc.h"
+#include "fsmonitor-settings.h"
 
 static void repo_cfg_bool(struct repository *r, const char *key, int *dest,
 			  int def)
@@ -36,6 +37,29 @@ void prepare_repo_settings(struct repository *r)
 	/* Defaults modified by feature.* */
 	if (experimental) {
 		r->settings.fetch_negotiation_algorithm = FETCH_NEGOTIATION_SKIPPING;
+
+		/*
+		 * Force enable the builtin FSMonitor (unless the repo
+		 * is incompatible or they've already selected it or
+		 * the hook version).  But only if they haven't
+		 * explicitly turned it off -- so only if our config
+		 * value is UNSET.
+		 *
+		 * lookup_fsmonitor_settings() and check_for_ipc() do
+		 * not distinguish between explicitly set FALSE and
+		 * UNSET, so we re-test for an UNSET config key here.
+		 *
+		 * I'm not sure I want to fix fsmonitor-settings.c to
+		 * have more than one _DISABLED state since our usage
+		 * here is only to support this experimental period
+		 * (and I don't want to overload the _reason field
+		 * because it describes incompabilities).
+		 */
+		if (manyfiles &&
+		    fsmonitor_ipc__is_supported()  &&
+		    fsm_settings__get_mode(r) == FSMONITOR_MODE_DISABLED &&
+		    repo_config_get_bool(r, "core.usebuiltinfsmonitor", &value))
+			fsm_settings__set_ipc(r);
 	}
 	if (manyfiles) {
 		r->settings.index_version = 4;