diff --git a/docs/Makefile b/docs/Makefile
index f0827113a82754939541a7b903700e3f980f2fcf..32f7b43dac183f982b1c7fa9a3845cefad829a78 100644
--- a/docs/Makefile
+++ b/docs/Makefile
@@ -7,7 +7,7 @@
 
 # You can set these variables from the command line, and also
 # from the environment for the first two.
-SPHINXOPTS    ?= 
+SPHINXOPTS    ?= -W
 SPHINXBUILD   ?= sphinx-build
 SOURCEDIR     = .
 BUILDDIR      = _build