diff --git a/docs/Makefile b/docs/Makefile
index d4bb2cbb9eddb1bb1b4f366623044af8e4830919..2fded69ef22609c81433f29814271a37b46e4f8c 100644
--- a/docs/Makefile
+++ b/docs/Makefile
@@ -3,7 +3,7 @@
 
 # You can set these variables from the command line, and also
 # from the environment for the first two.
-SPHINXOPTS    ?=
+SPHINXOPTS    ?= -E
 SPHINXBUILD   ?= sphinx-build
 SOURCEDIR     = .
 BUILDDIR      = _build