diff --git a/CHANGELOG b/CHANGELOG
index 4876c42a..02ec9030 100644
--- a/CHANGELOG
+++ b/CHANGELOG
@@ -6,6 +6,10 @@ HISTORY
 
  ++ New features:
 
+  2011-07-21: Simon Goldschmidt
+  * sockets.c, opt.h: (bug #30185): added LWIP_FIONREAD_LINUXMODE that makes
+    ioctl/FIONREAD return the size of the next pending datagram.
+
   2011-06-26: Simon Goldschmidt (patch by Cameron Gutman)
   * tcp.c, tcp_out.c: bug #33604: added some more asserts to check that
     pcb->state != LISTEN
diff --git a/src/api/sockets.c b/src/api/sockets.c
index 9af71c4e..ba68e726 100644
--- a/src/api/sockets.c
+++ b/src/api/sockets.c
@@ -2330,13 +2330,38 @@ lwip_ioctl(int s, long cmd, void *argp)
   }
 
   switch (cmd) {
-#if LWIP_SO_RCVBUF
+#if LWIP_SO_RCVBUF || LWIP_FIONREAD_LINUXMODE
   case FIONREAD:
     if (!argp) {
       sock_set_errno(sock, EINVAL);
       return -1;
     }
+#if LWIP_FIONREAD_LINUXMODE
+    if (NETCONNTYPE_GROUP(netconn_type(sock->conn)) != NETCONN_TCP) {
+      struct pbuf *p;
+      if (sock->lastdata) {
+        p = ((struct netbuf *)sock->lastdata)->p;
+      } else {
+        struct netbuf *rxbuf;
+        err_t err;
+        if (sock->rcvevent <= 0) {
+          *((u16_t*)argp) = 0;
+        } else {
+          err = netconn_recv(sock->conn, &rxbuf);
+          if (err != ERR_OK) {
+            *((u16_t*)argp) = 0;
+          } else {
+            sock->lastdata = rxbuf;
+            *((u16_t*)argp) = rxbuf->p->tot_len;
+          }
+        }
+      }
+      return 0;
+    }
+#endif /* LWIP_FIONREAD_LINUXMODE */
 
+#if LWIP_SO_RCVBUF
+    /* we come here if either LWIP_FIONREAD_LINUXMODE==0 or this is a TCP socket */
     SYS_ARCH_GET(sock->conn->recv_avail, recv_avail);
     if (recv_avail < 0) {
       recv_avail = 0;
@@ -2358,7 +2383,10 @@ lwip_ioctl(int s, long cmd, void *argp)
     LWIP_DEBUGF(SOCKETS_DEBUG, ("lwip_ioctl(%d, FIONREAD, %p) = %"U16_F"\n", s, argp, *((u16_t*)argp)));
     sock_set_errno(sock, 0);
     return 0;
+#else /* LWIP_SO_RCVBUF */
+    break;
 #endif /* LWIP_SO_RCVBUF */
+#endif /* LWIP_SO_RCVBUF || LWIP_FIONREAD_LINUXMODE */
 
   case FIONBIO:
     val = 0;
@@ -2371,10 +2399,11 @@ lwip_ioctl(int s, long cmd, void *argp)
     return 0;
 
   default:
-    LWIP_DEBUGF(SOCKETS_DEBUG, ("lwip_ioctl(%d, UNIMPL: 0x%lx, %p)\n", s, cmd, argp));
-    sock_set_errno(sock, ENOSYS); /* not yet implemented */
-    return -1;
+    break;
   } /* switch (cmd) */
+  LWIP_DEBUGF(SOCKETS_DEBUG, ("lwip_ioctl(%d, UNIMPL: 0x%lx, %p)\n", s, cmd, argp));
+  sock_set_errno(sock, ENOSYS); /* not yet implemented */
+  return -1;
 }
 
 /** A minimal implementation of fcntl.
diff --git a/src/include/lwip/opt.h b/src/include/lwip/opt.h
index a8243b6a..911b6251 100644
--- a/src/include/lwip/opt.h
+++ b/src/include/lwip/opt.h
@@ -1443,6 +1443,18 @@
 #define SO_REUSE_RXTOALL                0
 #endif
 
+/**
+ * LWIP_FIONREAD_LINUXMODE==0 (default): ioctl/FIONREAD returns the amount of
+ * pending data in the network buffer. This is the way windows does it. It's
+ * the default for lwIP since it is smaller.
+ * LWIP_FIONREAD_LINUXMODE==1: ioctl/FIONREAD returns the size of the next
+ * pending datagram in bytes. This is the way linux does it. This code is only
+ * here for compatibility.
+ */
+#ifndef LWIP_FIONREAD_LINUXMODE
+#define LWIP_FIONREAD_LINUXMODE         0
+#endif
+
 /*
    ----------------------------------------
    ---------- Statistics options ----------