diff --git a/mainwindow.cpp b/mainwindow.cpp
index b72f30b98..674ee2c5f 100644
--- a/mainwindow.cpp
+++ b/mainwindow.cpp
@@ -141,7 +141,6 @@ extern "C" {
 }
 
 int volatile itone[NUM_ISCAT_SYMBOLS];  //Audio tones for all Tx symbols
-char volatile ft8msgbits[75];           //packed 75 bit ft8 message
 int volatile icw[NUM_CW_SYMBOLS];       //Dits for CW ID
 struct dec_data dec_data;               // for sharing with Fortran
 
@@ -3377,6 +3376,7 @@ void MainWindow::guiUpdate()
               foxTxSequencer();
             } else {
               m_i3bit=0;
+              char ft8msgbits[75 + 12]; //packed 75 bit ft8 message plus 12-bit CRC
               genft8_(message, MyGrid, &bcontest, &m_i3bit, msgsent, const_cast<char *> (ft8msgbits),
                       const_cast<int *> (itone), 22, 6, 22);
             }