diff --git a/net/checksum.c b/net/checksum.c
index b5016ab..d0fa424 100644
--- a/net/checksum.c
+++ b/net/checksum.c
@@ -60,6 +60,11 @@
     int hlen, plen, proto, csum_offset;
     uint16_t csum;
 
+    /* Ensure data has complete L2 & L3 headers. */
+    if (length < 14 + 20) {
+        return;
+    }
+
     if ((data[14] & 0xf0) != 0x40)
 	return; /* not IPv4 */
     hlen  = (data[14] & 0x0f) * 4;
@@ -77,8 +82,9 @@
 	return;
     }
 
-    if (plen < csum_offset+2)
-	return;
+    if (plen < csum_offset + 2 || 14 + hlen + plen > length) {
+        return;
+    }
 
     data[14+hlen+csum_offset]   = 0;
     data[14+hlen+csum_offset+1] = 0;