diff --git a/.azure-pipelines/docs-steps.yml b/.azure-pipelines/docs-steps.yml
index c0404aebdcc..460576cbc95 100644
--- a/.azure-pipelines/docs-steps.yml
+++ b/.azure-pipelines/docs-steps.yml
@@ -12,7 +12,7 @@ steps:
   inputs:
     versionSpec: '>=3.6'
 
-- script: python -m pip install sphinx~=1.6.1 blurb python-docs-theme
+- script: python -m pip install sphinx==1.8.1 blurb python-docs-theme
   displayName: 'Install build dependencies'
 
 - ${{ if ne(parameters.latex, 'true') }}:
diff --git a/Doc/Makefile b/Doc/Makefile
index 042f960b93e..50beac58ec3 100644
--- a/Doc/Makefile
+++ b/Doc/Makefile
@@ -12,7 +12,7 @@ PAPER        =
 SOURCES      =
 DISTVERSION  = $(shell $(PYTHON) tools/extensions/patchlevel.py)
 
-ALLSPHINXOPTS = -b $(BUILDER) -d build/doctrees -D latex_elements.papersize=$(PAPER) \
+ALLSPHINXOPTS = -b $(BUILDER) -d build/doctrees -W -D latex_elements.papersize=$(PAPER) \
                 $(SPHINXOPTS) . build/$(BUILDER) $(SOURCES)
 
 .PHONY: help build html htmlhelp latex text changes linkcheck \
diff --git a/Misc/NEWS.d/next/Build/2018-09-06-07-15-20.bpo-34081.cuSTnH.rst b/Misc/NEWS.d/next/Build/2018-09-06-07-15-20.bpo-34081.cuSTnH.rst
new file mode 100644
index 00000000000..af385bac231
--- /dev/null
+++ b/Misc/NEWS.d/next/Build/2018-09-06-07-15-20.bpo-34081.cuSTnH.rst
@@ -0,0 +1 @@
+Make Sphinx warnings as errors in the Docs Makefile.