diff --git a/docs/reference/pip_install.rst b/docs/reference/pip_install.rst
index 20963375a..27757637d 100644
--- a/docs/reference/pip_install.rst
+++ b/docs/reference/pip_install.rst
@@ -235,7 +235,7 @@ Since version 6.0, pip also supports specifers containing `environment markers
  ::
 
   SomeProject ==5.4 ; python_version < '2.7'
-  SomeProject; sys.platform == 'win32'
+  SomeProject; sys_platform == 'win32'
 
 Environment markers are supported in the command line and in requirements files.