diff --git a/src/coap_block.c b/src/coap_block.c
index f36d8bb840..fad031a4e9 100644
--- a/src/coap_block.c
+++ b/src/coap_block.c
@@ -2283,9 +2283,27 @@ coap_block_new_lg_crcv(coap_session_t *session, coap_pdu_t *pdu,
   uint64_t state_token = STATE_TOKEN_FULL(++session->tx_token, 1);
   size_t token_options = pdu->data ? (size_t)(pdu->data - pdu->token) :
                          pdu->used_size;
-  size_t data_len = lg_xmit ? lg_xmit->length :
-                    pdu->data ?
-                    pdu->used_size - (pdu->data - pdu->token) : 0;
+  size_t data_len;
+  int observe_action = -1;
+
+  if (lg_xmit) {
+    coap_opt_iterator_t opt_iter;
+    coap_opt_t *opt;
+
+    opt = coap_check_option(pdu, COAP_OPTION_OBSERVE, &opt_iter);
+
+    if (opt) {
+      observe_action = coap_decode_var_bytes(coap_opt_value(opt),
+                                             coap_opt_length(opt));
+    }
+  }
+  if (observe_action == COAP_OBSERVE_ESTABLISH) {
+    data_len = lg_xmit->length;
+  } else {
+    lg_xmit = NULL;
+    data_len = pdu->data ?
+               pdu->used_size - (pdu->data - pdu->token) : 0;
+  }
 
   lg_crcv = coap_malloc_type(COAP_LG_CRCV, sizeof(coap_lg_crcv_t));
 
diff --git a/src/coap_net.c b/src/coap_net.c
index 816b65c111..18de2e2c39 100644
--- a/src/coap_net.c
+++ b/src/coap_net.c
@@ -3569,7 +3569,7 @@ handle_request(coap_context_t *context, coap_session_t *session, coap_pdu_t *pdu
   if (session->block_mode & COAP_BLOCK_USE_LIBCOAP) {
     uint32_t block_mode = session->block_mode;
 
-    if (pdu->code == COAP_REQUEST_CODE_FETCH ||
+    if (observe ||
         resource->flags & COAP_RESOURCE_FLAGS_FORCE_SINGLE_BODY)
       session->block_mode |= COAP_BLOCK_SINGLE_BODY;
     if (coap_handle_request_put_block(context, session, pdu, response,
@@ -3617,10 +3617,10 @@ handle_request(coap_context_t *context, coap_session_t *session, coap_pdu_t *pdu
         uint8_t buf[4];
 
         coap_touch_observer(context, session, &pdu->actual_token);
-        coap_add_option_internal(response, COAP_OPTION_OBSERVE,
-                                 coap_encode_var_safe(buf, sizeof(buf),
-                                                      resource->observe),
-                                 buf);
+        coap_insert_option(response, COAP_OPTION_OBSERVE,
+                           coap_encode_var_safe(buf, sizeof(buf),
+                                                resource->observe),
+                           buf);
       }
     } else if (observe_action == COAP_OBSERVE_CANCEL) {
       coap_delete_observer_request(resource, session, &pdu->actual_token, pdu);