diff --git a/book/Makefile b/book/Makefile
index 8e84021..af41109 100644
--- a/book/Makefile
+++ b/book/Makefile
@@ -7,17 +7,24 @@
 # You can set these variables from the command line, and also
 # from the environment for the first two.
 CODESPELL ?= codespell
+EBOOK_VIEWER ?= ebook-viewer
 EPUBCHECK ?= epubcheck
 SPHINXOPTS    ?= -W
 SPHINXBUILD   ?= sphinx-build
 LYCHEE ?= lychee
 PRINTF ?= printf
+WATCHEXEC ?= watchexec
 SOURCEDIR     = source
 BUILDDIR      = build
 
 epub-check: clean epub
 	@$(EPUBCHECK) "$(BUILDDIR)/epub/"*.epub
 
+# use watchexec to rebuild the EPUB whenever a markdown file changes
+# this target kills *any* open instance of calibre's ebook-viewer, that is currently showing OpenPGPforapplicationdevelopers.epub
+epub-watch:
+	@$(WATCHEXEC) --shell bash -e css,md 'make clean epub && ev_pid="$$(pgrep -af "^python3.*ebook-viewer.*OpenPGPforapplicationdevelopers" | cut -f1 -d " ")" && if [[ -n "$$ev_pid" ]]; then kill -9 "$$ev_pid"; fi && $(EBOOK_VIEWER) $(BUILDDIR)/epub/OpenPGPforapplicationdevelopers.epub &'
+
 # Put it first so that "make" without argument is like "make help".
 help:
 	@$(SPHINXBUILD) -M help "$(SOURCEDIR)" "$(BUILDDIR)" $(SPHINXOPTS) $(O)