diff --git a/lib/decoding/tch_f_decoder_impl.cc b/lib/decoding/tch_f_decoder_impl.cc
index 467ffe9..cbb1481 100644
--- a/lib/decoding/tch_f_decoder_impl.cc
+++ b/lib/decoding/tch_f_decoder_impl.cc
@@ -155,11 +155,10 @@
 
                     pmt::pmt_t first_header_plus_burst = pmt::cdr(d_bursts[0]);
                     gsmtap_hdr * header = (gsmtap_hdr *)pmt::blob_data(first_header_plus_burst);
-                    header->type = GSMTAP_TYPE_UM;
-                    int8_t * header_content = (int8_t *)header;
                     int8_t header_plus_data[sizeof(gsmtap_hdr)+DATA_BYTES];
-                    memcpy(header_plus_data, header_content, sizeof(gsmtap_hdr));
+                    memcpy(header_plus_data, header, sizeof(gsmtap_hdr));
                     memcpy(header_plus_data+sizeof(gsmtap_hdr), outmsg, DATA_BYTES);
+                    ((gsmtap_hdr*)header_plus_data)->type = GSMTAP_TYPE_UM;
 
                     pmt::pmt_t msg_binary_blob = pmt::make_blob(header_plus_data,DATA_BYTES+sizeof(gsmtap_hdr));
                     pmt::pmt_t msg_out = pmt::cons(pmt::PMT_NIL, msg_binary_blob);