diff --git a/Makefile b/Makefile
index ab39f6ce..a9b32189 100644
--- a/Makefile
+++ b/Makefile
@@ -25,6 +25,9 @@ JOBS = 4
 
 .PHONY: all
 all: $(SPHINX_CONF) $(VENV)/bin/activate
+ifneq "$(shell cd $(CPYTHON_CLONE) 2>/dev/null && git describe --contains --all HEAD)" "$(BRANCH)"
+	$(warning "Your ../cpython checkout is on the wrong branch, got $(shell cd $(CPYTHON_CLONE) 2>/dev/null && git describe --contains --all HEAD) expected $(BRANCH)")
+endif
 	mkdir -p $(CPYTHON_CLONE)/locales/$(LANGUAGE)/
 	ln -nfs $(shell readlink -f .) $(CPYTHON_CLONE)/locales/$(LANGUAGE)/LC_MESSAGES
 	$(MAKE) -C $(CPYTHON_CLONE)/Doc/ VENVDIR=$(VENV) PYTHON=$(PYTHON) SPHINXOPTS='-qaEW -j$(JOBS) -D locale_dirs=../locales -D language=$(LANGUAGE) -D gettext_compact=0 -D latex_engine=xelatex -D latex_elements.inputenc= -D latex_elements.fontenc=' $(MODE)