diff --git a/ports/Common.allports.mk b/ports/Common.allports.mk
index a8bcb0f..7e9d2e4 100644
--- a/ports/Common.allports.mk
+++ b/ports/Common.allports.mk
@@ -67,7 +67,7 @@ CFLAGS+=-I. \
 MBEDTLSDIR?=$(CONTRIBDIR)/../mbedtls
 ifneq (,$(wildcard $(MBEDTLSDIR)/include/mbedtls/*.h))
 LDFLAGS+=-L$(MBEDTLSDIR)/library -lmbedtls -lmbedcrypto -lmbedx509
-CFLAGS+=-I$(MBEDTLSDIR)/include -Wno-redundant-decls -DLWIP_HAVE_MBEDTLS=1
+CFLAGS+=-I$(MBEDTLSDIR)/include -Wno-redundant-decls -DLWIP_HAVE_MBEDTLS=1 -Wno-c90-c99-compat
 endif
 
 include $(CONTRIBDIR)/Filelists.mk