diff --git a/src/cryptonote_basic/cryptonote_format_utils.cpp b/src/cryptonote_basic/cryptonote_format_utils.cpp
index b062f4424..d87717bbe 100644
--- a/src/cryptonote_basic/cryptonote_format_utils.cpp
+++ b/src/cryptonote_basic/cryptonote_format_utils.cpp
@@ -1324,13 +1324,22 @@ namespace cryptonote
   crypto::hash get_sig_data(const block& b)
   {
     crypto::hash sig_data;
-    std::stringstream ss;
-    ss << (b.nonce + b.timestamp);
-    std::string d(ss.str());
-    crypto::cn_fast_hash(d.data(), d.size(), sig_data);
+    blobdata blob = get_block_hashing_blob_sig_data(b);
+    crypto::cn_fast_hash(blob.data(), blob.size(), sig_data);
     return sig_data;
   }
   //---------------------------------------------------------------
+  blobdata get_block_hashing_blob_sig_data(const block& b)
+  {
+    block_header tmp = static_cast<const block_header&>(b);
+    memset(&tmp.signature, 0, sizeof(tmp.signature));
+    blobdata blob = t_serializable_object_to_blob(tmp);
+    crypto::hash tree_root_hash = get_tx_tree_hash(b);
+    blob.append(reinterpret_cast<const char*>(&tree_root_hash), sizeof(tree_root_hash));
+    blob.append(tools::get_varint_data(b.tx_hashes.size()+1));
+    return blob;
+  }
+  //---------------------------------------------------------------
   std::vector<uint64_t> relative_output_offsets_to_absolute(const std::vector<uint64_t>& off)
   {
     std::vector<uint64_t> res = off;
diff --git a/src/cryptonote_basic/cryptonote_format_utils.h b/src/cryptonote_basic/cryptonote_format_utils.h
index dc2073c5a..7861242b8 100644
--- a/src/cryptonote_basic/cryptonote_format_utils.h
+++ b/src/cryptonote_basic/cryptonote_format_utils.h
@@ -122,6 +122,7 @@ namespace cryptonote
   bool get_block_hash(const block& b, crypto::hash& res);
   crypto::hash get_block_hash(const block& b);
   crypto::hash get_sig_data(const block& b);
+  blobdata get_block_hashing_blob_sig_data(const block& b);
   bool parse_and_validate_block_from_blob(const blobdata_ref& b_blob, block& b, crypto::hash *block_hash);
   bool parse_and_validate_block_from_blob(const blobdata_ref& b_blob, block& b);
   bool parse_and_validate_block_from_blob(const blobdata_ref& b_blob, block& b, crypto::hash &block_hash);