diff --git a/src/core/ipv4/icmp.c b/src/core/ipv4/icmp.c
index 7a0eca39..cf427b27 100644
--- a/src/core/ipv4/icmp.c
+++ b/src/core/ipv4/icmp.c
@@ -61,7 +61,7 @@ icmp_input(struct pbuf *p, struct netif *inp)
   
   iphdr = p->payload;
   hlen = IPH_HL(iphdr) * 4;
-  pbuf_header(p, -hlen);
+  pbuf_header(p, -((s16_t)hlen));
 
   type = *((u8_t *)p->payload);
 
diff --git a/src/core/tcp_in.c b/src/core/tcp_in.c
index df3b89a9..1ddaaf7d 100644
--- a/src/core/tcp_in.c
+++ b/src/core/tcp_in.c
@@ -106,8 +106,8 @@ tcp_input(struct pbuf *p, struct netif *inp)
 
   iphdr = p->payload;
   tcphdr = (struct tcp_hdr *)((u8_t *)p->payload + IPH_HL(iphdr) * 4);
-
-  pbuf_header(p, -(IPH_HL(iphdr) * 4));
+ 
+  pbuf_header(p, -((s16_t)(IPH_HL(iphdr) * 4)));
   
   /* Don't even process incoming broadcasts/multicasts. */
   if(ip_addr_isbroadcast(&(iphdr->dest), &(inp->netmask)) ||
@@ -116,7 +116,6 @@ tcp_input(struct pbuf *p, struct netif *inp)
     return;
   }
 
-
   /* Verify TCP checksum. */
   if(inet_chksum_pseudo(p, (struct ip_addr *)&(iphdr->src),
 			(struct ip_addr *)&(iphdr->dest),
diff --git a/src/core/udp.c b/src/core/udp.c
index 58774754..aea61330 100644
--- a/src/core/udp.c
+++ b/src/core/udp.c
@@ -171,7 +171,7 @@ udp_input(struct pbuf *p, struct netif *inp)
 
   iphdr = p->payload;
 
-  pbuf_header(p, -(UDP_HLEN + IPH_HL(iphdr) * 4));
+  pbuf_header(p, -((s16_t)(UDP_HLEN + IPH_HL(iphdr) * 4)));
 
   udphdr = (struct udp_hdr *)((u8_t *)p->payload - UDP_HLEN);