diff --git a/firmware-and-api-reference/pycom/network/sigfox.md b/firmware-and-api-reference/pycom/network/sigfox.md
index e7b49db..ceece16 100644
--- a/firmware-and-api-reference/pycom/network/sigfox.md
+++ b/firmware-and-api-reference/pycom/network/sigfox.md
@@ -241,6 +241,10 @@ s.recv(32)
 
 To communicate between two Sigfox capable devices, it may be used in FSK mode. Two devices are required to be set to the same frequency, both using FSK.
 
+{% hint style="info" %}
+`Sigfox.FSK` mode is not supported on LoPy 4 and FiPy.
+{% endhint %}
+
 **Device 1**:
 
 ```python