diff --git a/Makefile b/Makefile
index 13ecff1..12edf93 100644
--- a/Makefile
+++ b/Makefile
@@ -101,7 +101,7 @@ clobber: clean
 	rm -f ot-recorder ocat
 
 mdb/liblmdb.a:
-	(cd mdb && $(MAKE) liblmdb.a CC=$(CC) CFLAGS=$(MDBFLAGS) )
+	(cd mdb && $(MAKE) liblmdb.a CC=$(CC) CFLAGS="$(MDBFLAGS)" )
 
 install: ot-recorder ocat
 	mkdir -p $(DESTDIR)$(INSTALLDIR)/bin