diff --git a/Makefile b/Makefile
index dc90ac7..91c62fd 100644
--- a/Makefile
+++ b/Makefile
@@ -87,7 +87,7 @@ $(lw_source_tarball) : $(lw_source_dir)
 	sha256sum $(lw_source_tarball) > $(lw_source_tarball).sha256sum
 	cat $(lw_source_tarball).sha256sum
 	[ "$(SIGNING_KEY)" != "" ] && cp -v $(SIGNING_KEY) pk.asc ; true
-	if [[ -f pk.asc ]]; then gpg --import pk.asc; gpg --detach-sign $(lw_source_tarball); fi
+	if [ -f pk.asc ]; then gpg --import pk.asc; gpg --detach-sign $(lw_source_tarball); fi
 	ls -lh $(lw_source_tarball).sig