diff --git a/admin_manual/Makefile b/admin_manual/Makefile
index 8bcf2db09..805a74fa1 100644
--- a/admin_manual/Makefile
+++ b/admin_manual/Makefile
@@ -52,7 +52,7 @@ html-release:
 	@echo "Build finished. The HTML pages are in $(BUILDDIR)/html/release."
 
 html-com:
-	$(SPHINXBUILD) -b html -D html_theme='sphinx_rtd_theme' $(ALLSPHINXOPTS) $(BUILDDIR)/html/com
+	$(SPHINXBUILD) -W -b html -D html_theme='sphinx_rtd_theme' $(ALLSPHINXOPTS) $(BUILDDIR)/html/com
 	@echo
 	@echo "Build finished. The HTML pages are in $(BUILDDIR)/html/com."
 
diff --git a/developer_manual/Makefile b/developer_manual/Makefile
index 8bcf2db09..805a74fa1 100644
--- a/developer_manual/Makefile
+++ b/developer_manual/Makefile
@@ -52,7 +52,7 @@ html-release:
 	@echo "Build finished. The HTML pages are in $(BUILDDIR)/html/release."
 
 html-com:
-	$(SPHINXBUILD) -b html -D html_theme='sphinx_rtd_theme' $(ALLSPHINXOPTS) $(BUILDDIR)/html/com
+	$(SPHINXBUILD) -W -b html -D html_theme='sphinx_rtd_theme' $(ALLSPHINXOPTS) $(BUILDDIR)/html/com
 	@echo
 	@echo "Build finished. The HTML pages are in $(BUILDDIR)/html/com."
 
diff --git a/user_manual/Makefile b/user_manual/Makefile
index 4ab3dd293..924872fee 100644
--- a/user_manual/Makefile
+++ b/user_manual/Makefile
@@ -58,7 +58,7 @@ add-lang-to-versions-template-%:
 html-all: $(foreach lang, $(LANGS), html-lang-$(lang))
 
 html-lang-%:    
-	$(SPHINXBUILD) -b html -D html_theme='sphinx_rtd_theme' -D language=$* $(ALLSPHINXOPTS) $(BUILDDIR)/html/$*
+	$(SPHINXBUILD) -W -b html -D html_theme='sphinx_rtd_theme' -D language=$* $(ALLSPHINXOPTS) $(BUILDDIR)/html/$*
 	@echo "Build finished for LANG=$*. The HTML pages are in $(BUILDDIR)/html/$*."
 
 merge-folders: