diff --git a/slirp/socket.c b/slirp/socket.c
index 280050a..e603164 100644
--- a/slirp/socket.c
+++ b/slirp/socket.c
@@ -51,10 +51,12 @@ socreate(Slirp *slirp)
   so = (struct socket *)malloc(sizeof(struct socket));
   if(so) {
     memset(so, 0, sizeof(struct socket));
+    so->canary1 = 0xdeadbeef;
     so->so_state = SS_NOFDREF;
     so->s = -1;
     so->slirp = slirp;
     so->pollfds_idx = -1;
+    so->canary2 = 0xbe3fd3ad;
   }
   return(so);
 }
@@ -67,6 +69,14 @@ sofree(struct socket *so)
 {
   Slirp *slirp = so->slirp;
 
+  if (so->s == -1234)
+    fprintf(stderr,"oops, re-freeing a freed socket!\n");
+  if (so->canary1 != 0xdeadbeef)
+    fprintf(stderr,"oops, canary1 bogus!\n");
+  if (so->canary2 != 0xbe3fd3ad)
+    fprintf(stderr,"oops, canary2 bogus!\n");
+  so->s = -1234;
+
   if (so->so_emu==EMU_RSH && so->extra) {
 	sofree(so->extra);
 	so->extra=NULL;
diff --git a/slirp/socket.h b/slirp/socket.h
index 8feed2a..14fac1c 100644
--- a/slirp/socket.h
+++ b/slirp/socket.h
@@ -17,6 +17,7 @@
 
 struct socket {
   struct socket *so_next,*so_prev;      /* For a linked list of sockets */
+  int canary1;
 
   int s;                           /* The actual socket */
 
@@ -70,6 +71,7 @@ struct socket {
   struct sbuf so_rcv;		/* Receive buffer */
   struct sbuf so_snd;		/* Send buffer */
   void * extra;			/* Extra pointer */
+  int canary2;
 };