diff --git a/source/_integrations/tradfri.markdown b/source/_integrations/tradfri.markdown
index 464ba64bff5..d3fdcbd1c18 100644
--- a/source/_integrations/tradfri.markdown
+++ b/source/_integrations/tradfri.markdown
@@ -47,6 +47,10 @@ allow_tradfri_groups:
 
 ## Troubleshooting
 
+### Incorrect security key
+
+`Fatal DTLS error: code 20` might indicate a missing or incorrect security key. Pay close attention as e.g., "I" and "l" can easily be confused.
+
 ### Firmware updates
 
 After updating your IKEA Trådfri Gateway firmware it might be necessary to repeat the configuration process. One error you might experience after a firmware update is `Fatal DTLS error: code 115`. If you encounter problems: