diff --git a/src/H5SM.c b/src/H5SM.c
index 8b5faf9448..efd1ea9bf3 100755
--- a/src/H5SM.c
+++ b/src/H5SM.c
@@ -816,8 +816,8 @@ H5SM_try_share(H5F_t *f, hid_t dxpl_id, unsigned type_id, void *mesg)
     } /* end if */
 
     /* If the message isn't big enough, don't bother sharing it */
-    if(0 == (mesg_size = H5O_msg_mesg_size(f, type_id, mesg, (size_t)0)))
-	HGOTO_ERROR(H5E_OHDR, H5E_BADMESG, FAIL, "unable to get OH message size")
+    if(0 == (mesg_size = H5O_msg_raw_size(f, type_id, TRUE, mesg)))
+        HGOTO_ERROR(H5E_OHDR, H5E_BADMESG, FAIL, "unable to get OH message size")
     if(mesg_size < table->indexes[index_num].min_mesg_size)
         HGOTO_DONE(FALSE);
 
@@ -1223,14 +1223,9 @@ H5SM_delete_from_index(H5F_t *f, hid_t dxpl_id, H5SM_index_header_t *header,
     /* Prepare user data for fractal heap 'op' callback */
     udata.type_id = type_id;
 
-    /* Compute the hash value for the B-tree lookup */
-    if(H5HF_op(fheap, dxpl_id, &(mesg->u.heap_id), H5SM_get_hash_fh_cb, &udata) < 0)
-        HGOTO_ERROR(H5E_HEAP, H5E_CANTGET, FAIL, "can't access message in fractal heap")
-
-
     /* Set up key for message to be deleted. */
     key.message.fheap_id = mesg->u.heap_id;
-    key.message.hash = udata.hash;
+    key.message.hash = 0; /* Only needed for B-tree lookup */
     key.message.ref_count = 0;  /* Refcount isn't relevant here */
 
     key.encoding = NULL;
@@ -1259,6 +1254,12 @@ H5SM_delete_from_index(H5F_t *f, hid_t dxpl_id, H5SM_index_header_t *header,
     {
         HDassert(header->index_type == H5SM_BTREE);
 
+        /* Compute the hash value for the B-tree lookup */
+        if(H5HF_op(fheap, dxpl_id, &(mesg->u.heap_id), H5SM_get_hash_fh_cb, &udata) < 0)
+            HGOTO_ERROR(H5E_HEAP, H5E_CANTGET, FAIL, "can't access message in fractal heap")
+
+        key.message.hash = udata.hash;
+
         /* If this returns failure, it means that the message wasn't found.
          * If it succeeds, a copy of the modified message will be returned. */
         if(H5B2_modify(f, dxpl_id, H5SM_INDEX, header->index_addr, &key, H5SM_decr_ref, &message) <0)
@@ -1577,13 +1578,9 @@ H5SM_get_refcount(H5F_t *f, hid_t dxpl_id, unsigned type_id,
     /* Prepare user data for callback */
     udata.type_id = type_id;
 
-    /* Compute the hash value for the B-tree lookup */
-    if(H5HF_op(fheap, dxpl_id, &(sh_mesg->u.heap_id), H5SM_get_hash_fh_cb, &udata) < 0)
-        HGOTO_ERROR(H5E_HEAP, H5E_CANTGET, FAIL, "can't access message in fractal heap")
-
     /* Set up key for message to locate */
     key.message.fheap_id = sh_mesg->u.heap_id;
-    key.message.hash = udata.hash;
+    key.message.hash = 0; /* Only needed for B-tree lookup */
     key.message.ref_count = 0; /* Ref count isn't needed to find message */
 
     key.encoding = NULL;
@@ -1609,6 +1606,12 @@ H5SM_get_refcount(H5F_t *f, hid_t dxpl_id, unsigned type_id,
     {
         HDassert(header->index_type == H5SM_BTREE);
 
+        /* Compute the hash value for the B-tree lookup */
+        if(H5HF_op(fheap, dxpl_id, &(sh_mesg->u.heap_id), H5SM_get_hash_fh_cb, &udata) < 0)
+            HGOTO_ERROR(H5E_HEAP, H5E_CANTGET, FAIL, "can't access message in fractal heap")
+
+        key.message.hash = udata.hash;
+
         /* Look up the message in the v2 B-tree */
         if(H5B2_find(f, dxpl_id, H5SM_INDEX, header->index_addr, &key, H5SM_get_refcount_bt2_cb, &message) < 0)
 	    HGOTO_ERROR(H5E_SOHM, H5E_NOTFOUND, FAIL, "message not in index")
diff --git a/src/H5SMbtree2.c b/src/H5SMbtree2.c
index f1d12da5df..908729a270 100755
--- a/src/H5SMbtree2.c
+++ b/src/H5SMbtree2.c
@@ -143,14 +143,26 @@ H5SM_message_compare(const void *rec1, const void *rec2)
      */
     /* JAMES HDassert(mesg->ref_count > 0); */
 
+    /* If the key has an fheap ID, we're looking for a message that's
+     * already in the index; if the fheap ID matches, we've found the message
+     * and can stop immediately.
+     * This means that list indexes that don't care about ordering can
+     * pass in bogus hash values and they'll still get a match if the heap
+     * IDs are the same.
+     */
+    if(key->encoding_size == 0)
+    {
+        HDassert(key->encoding == NULL);
+        if(key->message.fheap_id == mesg->fheap_id)
+            HGOTO_DONE(0);
+    }
+
     hash_diff = key->message.hash;
     hash_diff -= mesg->hash;
 
     /* If the hash values match, make sure the messages are really the same */
     if(0 == hash_diff) {
-        /* Compare either the heap_ids directly (if the key has one)
-         * or the encoded buffers
-         */
+        /* Compare the encoded buffers or the fheap IDs */
         if(key->encoding_size == 0)
         {
             HDassert(key->encoding == NULL);
@@ -182,6 +194,7 @@ H5SM_message_compare(const void *rec1, const void *rec2)
             ret_value = -1;
     }
 
+done:
     FUNC_LEAVE_NOAPI(ret_value)
 } /* end H5SM_message_compare */
 
diff --git a/test/tsohm.c b/test/tsohm.c
index 7361f3e707..f0a37286eb 100644
--- a/test/tsohm.c
+++ b/test/tsohm.c
@@ -141,6 +141,9 @@ typedef struct size2_helper_struct {
 #define DELETE_NUM_MESGS 7
 #define HALF_DELETE_NUM_MESGS 3
 #define DELETE_DIMS {1,1,1,1,1,1,1}
+#define DELETE_MIN_MESG_SIZE 10
+#define DELETE_MAX_MESG_SIZE 60
+
 
 /* Number of dimensions in extend_dset test */
 #define EXTEND_NDIMS 2
@@ -2630,7 +2633,6 @@ static void delete_helper(hid_t fcpl_id, hid_t *dspace_id, hid_t *dcpl_id)
     CHECK_I(ret, "H5Fclose");
     norm_filesize = h5_get_file_size(FILENAME);
 
-
     /* Create a new file with messages 0 to (HALF_DELETE_NUM_MESGS - 1) */
     file_id = H5Fcreate(FILENAME, H5F_ACC_TRUNC, fcpl_id, H5P_DEFAULT);
     CHECK_I(file_id, "H5Fcreate");
@@ -2708,7 +2710,7 @@ test_sohm_delete(void)
      */
    for(x=0; x<DELETE_NUM_MESGS; ++x) {
         dspace_id[x] = H5Screate_simple(x + 1, dims, dims);
-        CHECK_I(dspace_id[x], "H5Screate_simple");        
+        CHECK_I(dspace_id[x], "H5Screate_simple");
     }
 
     /* Create a number of different filter pipelines. */
@@ -2752,7 +2754,6 @@ test_sohm_delete(void)
     /* Test that messages can be created and deleted properly */
     delete_helper(fcpl_id, dspace_id, dcpl_id);
 
-
     /* Use B-tree indexes */
     ret = H5Pset_shared_mesg_phase_change(fcpl_id, 0, 0);
     CHECK_I(ret, "H5Pset_shared_mesg_phase_change");
@@ -2793,6 +2794,18 @@ test_sohm_delete(void)
 
     delete_helper(fcpl_id, dspace_id, dcpl_id);
 
+
+    /* Test with varying message sizes (ideally, so some messages are too
+     * small to be written but some are big enough that they are still written
+     */
+    ret = H5Pset_shared_mesg_nindexes(fcpl_id, 1);
+    CHECK_I(ret, "H5Pset_shared_mesg_nindexes");
+    for(x=DELETE_MIN_MESG_SIZE; x<=DELETE_MAX_MESG_SIZE; x += 10) {
+        ret = H5Pset_shared_mesg_index(fcpl_id, 0, H5O_MESG_ALL_FLAG, (size_t) x);
+        CHECK_I(ret, "H5Pset_shared_mesg_phase_change");
+        delete_helper(fcpl_id, dspace_id, dcpl_id);
+    }
+
     /* Cleanup */
     ret = H5Pclose(fcpl_id);
     CHECK_I(ret, "H5Pclose");
@@ -2946,6 +2959,7 @@ test_sohm_delete_revert(void)
     ret = H5Pset_shared_mesg_index(fcpl_id, 0, H5O_MESG_ALL_FLAG, 10);
     CHECK_I(ret, "H5Pset_shared_mesg_index");
     ret = H5Pset_shared_mesg_phase_change(fcpl_id, 10, 5);
+    CHECK_I(ret, "H5Pset_shared_mesg_phase_change");
 
     test_sohm_delete_revert_helper(fcpl_id);
 
@@ -2962,6 +2976,14 @@ test_sohm_delete_revert(void)
     CHECK_I(ret, "H5Pset_shared_mesg_phase_change");
     test_sohm_delete_revert_helper(fcpl_id);
 
+
+    /* Try with shared messages enabled, but when messages are too big
+     * to be shared.
+     */
+    ret = H5Pset_shared_mesg_index(fcpl_id, 0, H5O_MESG_ALL_FLAG, 35);
+    CHECK_I(ret, "H5Pset_shared_mesg_phase_change");
+    test_sohm_delete_revert_helper(fcpl_id);
+
     ret = H5Pclose(fcpl_id);
     CHECK_I(ret, "H5Pclose");
 }
@@ -3330,7 +3352,6 @@ test_sohm(void)
 {
     /* Output message about test being performed */
     MESSAGE(5, ("Testing Shared Object Header Messages\n"));
-
     test_sohm_fcpl();		/* Test SOHMs and file creation plists */
     test_sohm_size1();          /* Tests the sizes of files with one SOHM */
     test_sohm_attrs();          /* Tests shared messages in attributes */