diff --git a/Compatibility-issues.md b/Compatibility-issues.md
index a486983..1561d9f 100644
--- a/Compatibility-issues.md
+++ b/Compatibility-issues.md
@@ -152,4 +152,17 @@ They are located here on Windows:
 
 ```
 %LOCALAPPDATA%\Arduino15\packages\arduino\hardware\samd\1.6.6\cores\arduino\USB
-```
\ No newline at end of file
+```
+
+## GCC warning: ignoring packed attribute because of unpacked non-POD field
+
+If you pass the flag `--fpack-struct` to the compiler, it will generate the following warning:
+
+```
+warning: ignoring packed attribute because of unpacked non-POD field
+```
+
+No solution has been found so far: you need to remove that flag if you want to get rid of that warning.
+
+See issue [#255](https://github.com/bblanchon/ArduinoJson/issues/255)
+