diff --git a/hgext/fsmonitor/__init__.py b/hgext/fsmonitor/__init__.py
--- a/hgext/fsmonitor/__init__.py
+++ b/hgext/fsmonitor/__init__.py
@@ -777,6 +777,18 @@
                       'extension and has been disabled.\n') % ext)
             return
 
+    enabled = None
+    if 'HGWATCHMAN_ENABLE' in encoding.environ:
+        enabled = encoding.environ['HGWATCHMAN_ENABLE'].lower()
+
+    if enabled == 'true' or enabled == '':
+        pass
+    elif enabled == 'false':
+        return
+    else:
+        if not ui.interactive():
+            return
+
     if repo.local():
         # We don't work with subrepos either.
         #