diff --git a/build.sh b/build.sh
index f2a966b..e78a600 100755
--- a/build.sh
+++ b/build.sh
@@ -1,3 +1,3 @@
-rm *.pdf
+[ -n "$(ls *.pdf 2>/dev/null)" ] && rm *.pdf
 OUT="cooganl-sound-hacking-v.$(git rev-list --count master).pdf"
 groff -R -Kutf8 -mom -Tpdf 00-front.mom 01-preface.mom 02-microsound.mom 03-convolution.mom 04-phase_vocoding.mom 05-alternative_tunings.mom > $OUT