diff --git a/Source/portable/MPLAB/PIC24_dsPIC/port.c b/Source/portable/MPLAB/PIC24_dsPIC/port.c
index 241c47206..fb19e586e 100644
--- a/Source/portable/MPLAB/PIC24_dsPIC/port.c
+++ b/Source/portable/MPLAB/PIC24_dsPIC/port.c
@@ -260,7 +260,7 @@ void vPortEndScheduler( void )
  */
 static void prvSetupTimerInterrupt( void )
 {
-const unsigned long ulCompareMatch = ( configCPU_CLOCK_HZ / portTIMER_PRESCALE ) / configTICK_RATE_HZ;
+const unsigned long ulCompareMatch = ( ( configCPU_CLOCK_HZ / portTIMER_PRESCALE ) / configTICK_RATE_HZ ) - 1;
 
 	/* Prescale of 8. */
 	T1CON = 0;