diff --git a/build.sh b/build.sh
index 81d6abd..7ad2712 100755
--- a/build.sh
+++ b/build.sh
@@ -4,7 +4,9 @@ if [ ! -e config.h ]; then
   cp config.def.h config.h
 fi
 
-clang-format -i ./*.c ./*.h ./*/*.c ./*/*.h
+if which clang-format > /dev/null; then
+  clang-format -i ./*.c ./*.h ./*/*.c ./*/*.h
+fi
 
 mk clean
 mk o.rio