diff --git a/sh.py b/sh.py
index 4a83a3ac..2976d6a5 100644
--- a/sh.py
+++ b/sh.py
@@ -28,7 +28,10 @@
 from collections.abc import Mapping
 
 import errno
-import fcntl
+try:
+    import fcntl
+except ImportError:
+    raise RuntimeError("This only works on *nix systems. Try Docker?")
 import gc
 import getpass
 import glob as glob_module