diff --git a/src/machine/machine_nrf51.go b/src/machine/machine_nrf51.go
index 701a915c..ed64c0c6 100644
--- a/src/machine/machine_nrf51.go
+++ b/src/machine/machine_nrf51.go
@@ -6,6 +6,8 @@ import (
 	"device/nrf"
 )
 
+const CPU_FREQUENCY = 16000000
+
 // Get peripheral and pin number for this GPIO pin.
 func (p GPIO) getPortPin() (*nrf.GPIO_Type, uint8) {
 	return nrf.GPIO, p.Pin
diff --git a/src/machine/machine_nrf52.go b/src/machine/machine_nrf52.go
index 70d12f55..8c73f6b8 100644
--- a/src/machine/machine_nrf52.go
+++ b/src/machine/machine_nrf52.go
@@ -7,6 +7,8 @@ import (
 	"unsafe"
 )
 
+const CPU_FREQUENCY = 64000000
+
 // Get peripheral and pin number for this GPIO pin.
 func (p GPIO) getPortPin() (*nrf.GPIO_Type, uint8) {
 	return nrf.P0, p.Pin
diff --git a/src/machine/machine_nrf52840.go b/src/machine/machine_nrf52840.go
index b10be826..507db983 100644
--- a/src/machine/machine_nrf52840.go
+++ b/src/machine/machine_nrf52840.go
@@ -7,6 +7,8 @@ import (
 	"unsafe"
 )
 
+const CPU_FREQUENCY = 64000000
+
 // Get peripheral and pin number for this GPIO pin.
 func (p GPIO) getPortPin() (*nrf.GPIO_Type, uint8) {
 	if p.Pin >= 32 {