diff --git a/Makefile.flags b/Makefile.flags
index ed42c2b..0c680f9 100644
--- a/Makefile.flags
+++ b/Makefile.flags
@@ -4,7 +4,10 @@
 
 BB_VER = $(VERSION).$(PATCHLEVEL).$(SUBLEVEL)$(EXTRAVERSION)
 
+# -std=gnu99 needed for [U]LLONG_MAX on some systems
+
 CPPFLAGS += \
+	-std=gnu99 \
 	-Iinclude -Ilibbb \
 	$(if $(KBUILD_SRC),-Iinclude2 -I$(srctree)/include) -I$(srctree)/libbb \
 	-include include/autoconf.h \