ignore error from `command`
diff --git a/Makefile.am b/Makefile.am
index 3d38148..5dde405 100644
--- a/Makefile.am
+++ b/Makefile.am
@@ -76,4 +76,4 @@ roundtrip: $(BZIP3)
./$(BZIP3) -v -feb 6 $(srcdir)/LICENSE $(builddir)/LICENSE.bz3
./$(BZIP3) -v -d $(builddir)/LICENSE.bz3 $(builddir)/LICENSE2
cmp $(srcdir)/LICENSE $(builddir)/LICENSE2
- command -v md5sum >/dev/null 2>&1 && md5sum $(builddir)/LICENSE.bz3
+ -command -v md5sum >/dev/null 2>&1 && md5sum $(builddir)/LICENSE.bz3
