diff --git a/hg b/hg
--- a/hg
+++ b/hg
@@ -28,8 +28,9 @@
 
 # enable importing on demand to reduce startup time
 try:
-    if sys.version_info[0] < 3 or sys.version_info >= (3, 6):
-        import hgdemandimport; hgdemandimport.enable()
+    if os.environ.get('HGDEMANDIMPORT') != 'disable':
+        if sys.version_info[0] < 3 or sys.version_info >= (3, 6):
+            import hgdemandimport; hgdemandimport.enable()
 except ImportError:
     sys.stderr.write("abort: couldn't find mercurial libraries in [%s]\n" %
                      ' '.join(sys.path))