diff --git a/docs/en_US/Makefile.sphinx b/docs/en_US/Makefile.sphinx
index 0af55b730..2c4bd410e 100644
--- a/docs/en_US/Makefile.sphinx
+++ b/docs/en_US/Makefile.sphinx
@@ -4,7 +4,7 @@
 # You can set these variables from the command line.
 PYTHON        = python
 SPHINXOPTS    =
-SPHINXBUILD   = sphinx-build
+SPHINXBUILD   = sphinx-build -W
 PAPER         =
 BUILDDIR      = _build