diff --git a/Makefile b/Makefile
index bbd9c274..0d1cbce5 100644
--- a/Makefile
+++ b/Makefile
@@ -22,8 +22,10 @@ VALGRIND_RUN ?= valgrind --tool=memcheck --gen-suppressions=all --leak-check=ful
 .PHONY: examples test valgrind mip_test
 
 ifeq "$(findstring ++,$(CC))" ""
+# $(CC) does not end with ++, i.e. we're using C. Apply C flags
 C_WARN ?= -Wmissing-prototypes -Wstrict-prototypes
 else
+# $(CC) ends with ++, i.e. we're using C++. Apply C++ flags
 C_WARN ?= -Wno-deprecated
 endif
 
@@ -81,8 +83,6 @@ test: Makefile mongoose.h $(SRCS)
 	$(CC) $(SRCS) $(CFLAGS) $(LDFLAGS) -o unit_test
 	ASAN_OPTIONS=$(ASAN_OPTIONS) $(RUN) ./unit_test
 
-#	$(CXX) $(SRCS) $(CFLAGS) $(LDFLAGS) $(CXX_WARN) -g -o unit_test
-
 coverage: CFLAGS += -coverage
 coverage: test
 	gcov -l -n *.gcno | sed '/^$$/d' | sed 'N;s/\n/ /'
@@ -107,12 +107,10 @@ vc98: Makefile mongoose.h $(SRCS)
 	$(DOCKER) mdashnet/vc98 wine cl $(SRCS) $(VCFLAGS) ws2_32.lib /Fe$@.exe
 	$(DOCKER) mdashnet/vc98 wine $@.exe
 
-# vc17: DEFS += -DMG_ENABLE_IPV6=1
 vc17: Makefile mongoose.h $(SRCS)
 	$(DOCKER) mdashnet/vc17 wine64 cl $(SRCS) $(VCFLAGS) ws2_32.lib /Fe$@.exe
 	$(DOCKER) mdashnet/vc17 wine64 $@.exe
 
-# vc22: DEFS += -DMG_ENABLE_IPV6=$(IPV6)
 vc22: Makefile mongoose.h $(SRCS)
 	$(DOCKER) mdashnet/vc22 wine64 cl $(SRCS) $(VCFLAGS) ws2_32.lib /Fe$@.exe
 	$(DOCKER) mdashnet/vc22 wine64 $@.exe
diff --git a/mip/mip.c b/mip/mip.c
index 60a416c3..d1150a1c 100644
--- a/mip/mip.c
+++ b/mip/mip.c
@@ -462,7 +462,7 @@ static void rx_dhcp(struct mip_if *ifp, struct pkt *pkt) {
   uint8_t *p = pkt->dhcp->options, *end = &pkt->raw.buf[pkt->raw.len];
   if (end < (uint8_t *) (pkt->dhcp + 1)) return;
   // MG_DEBUG(("DHCP %u", (unsigned) pkt->raw.len));
-  while (p < end && p[0] != 255) {
+  while (p + 1 < end && p[0] != 255) {
     if (p[0] == 1 && p[1] == sizeof(ifp->mask)) {
       memcpy(&mask, p + 2, sizeof(mask));
       // MG_DEBUG(("MASK %x", mask));