diff --git a/firmware/command_ctrl.ino b/firmware/command_ctrl.ino
index 44fd39c..3397ce8 100644
--- a/firmware/command_ctrl.ino
+++ b/firmware/command_ctrl.ino
@@ -207,7 +207,7 @@ void cc_startMeasurement()
       uint32_t a1_sum  = 0;
       uint16_t i = 0;
 
-      si5351.set_freq(freq * 100, SI5351_PLL_FIXED, SI5351_CLK0);
+      si5351.set_freq((uint64_t)freq * 100, SI5351_PLL_FIXED, SI5351_CLK0);
       si5351.output_enable(SI5351_CLK0, 1); // enable clock output 0
       delay(1);