diff --git a/include/ucore/mbuf.h b/include/ucore/mbuf.h
index 9d6129e..56efa1c 100644
--- a/include/ucore/mbuf.h
+++ b/include/ucore/mbuf.h
@@ -12,8 +12,8 @@
 enum UC_MBUF_FLAGS {
     UC_MBUF_FL_MALLOC        = 0x0001, //MBuf and MBuf->bufstart are seperatly malloc'd
     UC_MBUF_FL_MALLOC_BUF    = 0x0001, //MBuf is not malloc'd. MBuf->bufstart is malloc'd
-    UC_MBUF_FL_MALLOC_INLINE = 0x0002, //MBuf is one big malloc. Can't be resized
-    UC_MBUF_FL_STATIC        = 0x0004, //MBuf and MBuf->bustart is user controlled. Can't be resized
+    UC_MBUF_FL_MALLOC_INLINE = 0x0002, //MBuf is one big malloc. Can't be extended
+    UC_MBUF_FL_STATIC        = 0x0004, //MBuf and MBuf->bustart is user controlled. Can't be extended
 };
 
 struct MBuf {
@@ -187,6 +187,16 @@ uint8_t *uc_mbuf_push(struct MBuf *mbuf, uint32_t size);
  **/
 uint8_t *uc_mbuf_pull(struct MBuf *mbuf, uint32_t size);
 
+/** Add more tailroom to an mbuf.
+ * Can only be done with mbufs with either 
+ * UC_MBUF_FL_MALLOC or UC_MBUF_FL_MALLOC_BUF.
+ *
+ * @param len additional tailroom to add to mbuf
+ * @return 0 on success, otherwise failure
+ *
+ */
+int uc_mbuf_extend_tailroom(struct MBuf *mbuf, uint32_t len);
+
 /** Get a pointer to the data of the buffer
  * 
  * @return pointer to the start of the data (head)
diff --git a/src/mbuf.c b/src/mbuf.c
index 865612a..d77dd7b 100644
--- a/src/mbuf.c
+++ b/src/mbuf.c
@@ -1,4 +1,5 @@
 #include <string.h>
+#include <assert.h>
 #include <stdlib.h>
 #include "ucore/mbuf.h"
 
@@ -119,3 +120,81 @@ struct MBuf *uc_mbuf_copy_data(struct MBuf *mbuf)
     return copy;
 }
 
+int uc_mbuf_extend_tailroom(struct MBuf *mbuf, uint32_t len)
+{
+    uint32_t tot_len;
+    uint32_t headroom_len;
+    uint32_t data_len;
+    uint32_t tailroom_len;
+    uint8_t *new_data;
+    uint32_t p1_off;
+    uint32_t p2_off;
+    uint32_t p3_off;
+    uint32_t p4_off;
+
+    if ((mbuf->flags & (UC_MBUF_FL_MALLOC | UC_MBUF_FL_MALLOC_BUF)) == 0) {
+        return -1;
+    }
+    
+    headroom_len = uc_mbuf_headroom(mbuf);
+    data_len     = uc_mbuf_len(mbuf);
+    tailroom_len = uc_mbuf_tailroom(mbuf);
+    tot_len = headroom_len +
+                  data_len     +
+                  tailroom_len;
+
+    if (tot_len + len < tot_len) {
+        //overflowed
+        return -2;
+    }
+    
+    tot_len += len;
+    
+    //need to re-adjust p1-p4 after the realloc
+    //This assumes the user controlled p1-p4 really are
+    //set to point into the data, but we document they have
+    //to be.
+    if (mbuf->p1 != NULL) {
+        p1_off = (uint32_t)(mbuf->p1 - mbuf->bufstart);
+    }
+    if (mbuf->p2 != NULL) {
+        p2_off = (uint32_t)(mbuf->p2 - mbuf->bufstart);
+    }
+    if (mbuf->p3 != NULL) {
+        p3_off = (uint32_t)(mbuf->p3 - mbuf->bufstart);
+    }
+    if (mbuf->p4 != NULL) {
+        p4_off = (uint32_t)(mbuf->p4 - mbuf->bufstart);
+    }
+
+    assert(tot_len >= mbuf->allocated);
+
+    new_data = realloc(mbuf->bufstart, tot_len);
+    if (new_data == NULL) {
+        return -3;
+    }
+
+    mbuf->allocated = tot_len;
+    mbuf->bufstart = new_data;
+    mbuf->head = mbuf->bufstart + headroom_len;
+    mbuf->tail = mbuf->bufstart + headroom_len + data_len;
+
+    assert(uc_mbuf_len(mbuf) == data_len);
+    assert(uc_mbuf_tailroom(mbuf) >= tailroom_len);
+
+    if (mbuf->p1 != NULL) {
+        mbuf->p1 = mbuf->bufstart + p1_off;
+    }
+    if (mbuf->p2 != NULL) {
+        mbuf->p2 = mbuf->bufstart + p2_off;
+    }
+    if (mbuf->p3 != NULL) {
+        mbuf->p3 = mbuf->bufstart + p3_off;
+    }
+    if (mbuf->p4 != NULL) {
+        mbuf->p4 = mbuf->bufstart + p4_off;
+    }
+
+    return 0;
+
+}
diff --git a/test/test_mbuf.c b/test/test_mbuf.c
index badfab2..dcdb4b1 100644
--- a/test/test_mbuf.c
+++ b/test/test_mbuf.c
@@ -1,5 +1,6 @@
 #include <check.h>
 #include <string.h>
+#include <stdlib.h>
 #include <ucore/mbuf.h>
 
 
@@ -240,6 +241,58 @@ START_TEST (test_mbuf_static)
 
 END_TEST
 
+START_TEST (test_mbuf_extend_tailroom)
+    struct MBuf *mbuf;
+    uint8_t *data;
+    void *filler;
+    int rc;
+    
+    mbuf = uc_mbuf_new_hr(5,2);
+    fail_if(mbuf == NULL);
+
+    data = uc_mbuf_put(mbuf, 5);
+    fail_if(data == NULL);
+    memcpy((char*)data, "hello", 5);
+    mbuf->p1 = mbuf->tail;
+
+    data = uc_mbuf_put(mbuf, 6);
+    fail_if(data != NULL);
+
+    filler = malloc(5); //just a hope, so realloc also moves..
+    rc = uc_mbuf_extend_tailroom(mbuf, 1024);
+    ck_assert_int_eq(rc, 0);
+    ck_assert_int_eq(uc_mbuf_tailroom(mbuf), 1024);
+    ck_assert_int_eq(uc_mbuf_headroom(mbuf), 2);
+    ck_assert_int_eq(uc_mbuf_len(mbuf), 5);
+
+    //should work now
+    data = uc_mbuf_put(mbuf, 6);
+    fail_if(data == NULL);
+    strcpy((char*)data, "world");
+    ck_assert_str_eq((const char*)mbuf->head, "helloworld");
+    ck_assert_str_eq((const char*)mbuf->p1, "world");
+
+    uc_mbuf_free(mbuf);
+    free(filler);
+
+END_TEST
+
+START_TEST (test_mbuf_extend_tailroom_wrong_type)
+    struct MBuf *mbuf;
+    uint8_t *data;
+    int rc;
+    
+    mbuf = uc_mbuf_new_inline(10);
+    fail_if(mbuf == NULL);
+
+    rc = uc_mbuf_extend_tailroom(mbuf, 1024);
+    ck_assert_int_ne(rc, 0);
+
+    fail_if(data == NULL);
+
+    uc_mbuf_free(mbuf);
+
+END_TEST
 
 
 Suite *mbuf_suite(void)
@@ -258,6 +311,8 @@ Suite *mbuf_suite(void)
     tcase_add_test(tc, test_mbuf_copy);
     tcase_add_test(tc, test_mbuf_zero);
     tcase_add_test(tc, test_mbuf_static);
+    tcase_add_test(tc, test_mbuf_extend_tailroom);
+    tcase_add_test(tc, test_mbuf_extend_tailroom_wrong_type);
 
     suite_add_tcase(s, tc);