diff --git a/STM32F1/cores/maple/tone.cpp b/STM32F1/cores/maple/tone.cpp
index b249a78..c179c34 100644
--- a/STM32F1/cores/maple/tone.cpp
+++ b/STM32F1/cores/maple/tone.cpp
@@ -60,7 +60,7 @@ uint8_t tone_ntimer = TONE_TIMER;               // timer used to generate freque
 bool tone_state = true;             // last pin state for toggling
 short tone_pin = -1;                // pin for outputting sound
 short tone_freq = 444;              // tone frequency (0=pause)
-volatile uint32_t tone_nhw = 0;              // tone duration in number of half waves
+volatile uint32_t tone_nhw = 0;     // tone duration in number of half waves
 uint16_t tone_tcount = 0;           // time between handler calls in 1/36 usec
 uint16_t tone_ncount = 0;           // handler call between toggling
 uint16_t tone_n = 0;                // remaining handler calls before toggling
@@ -151,7 +151,7 @@ void tone(uint32_t pin, uint32_t freq, uint32_t duration) {
       tone_ncount = tone_n = (count>>16)+1; // number of 16-bit count chunk
       tone_tcount = count/tone_ncount;      // size of count chunk
       if(duration > 0) // number of half waves to be generated
-         tone_nhw = ((duration*freq)/1000)<<1;
+         tone_nhw = duration*freq*2/1000;
       else  // no duration specified, continuous sound until noTone() called
          tone_nhw = 0;