diff --git a/firmware/command_ctrl.ino b/firmware/command_ctrl.ino
index a031293..7ecd625 100644
--- a/firmware/command_ctrl.ino
+++ b/firmware/command_ctrl.ino
@@ -222,6 +222,12 @@ void cc_startMeasurement()
     uint32_t freq = 0;
     for (freq = start_freq; freq <= end_freq; freq += step_freq)
     {
+      if (freq > end_freq)
+      {
+        // prevent to step over the end frequency
+        // maybe the user is not allowed to send data in the frequency band
+        freq = end_freq;
+      }
       uint32_t a0_sum  = 0;
       uint32_t a1_sum  = 0;
       uint16_t i = 0;
@@ -268,6 +274,9 @@ void cc_startMeasurement()
       Serial.write(MSG_EOM2);
 
       si5351.output_enable(SI5351_CLK0, 0); // disable clock output 0
+
+      if (freq >= end_freq)
+        break; // abort the loop because all is done
     }
 
     // 5. send a measurement end message to the host