diff --git a/mbed-cortex-porting.md b/mbed-cortex-porting.md
index 7e7cb3e28a6..a2a106c6deb 100644
--- a/mbed-cortex-porting.md
+++ b/mbed-cortex-porting.md
@@ -1,5 +1,9 @@
 ## compile error: cstddef
-with arm-none-eabi-gcc (4.8.2-14ubuntu1+6) 4.8.2
+Experienced this with arm-none-eabi-gcc (4.8.2-14ubuntu1+6) 4.8.2 on ubuntu 14.04.
+
+And resolved with 4.9.3 installed from:
+https://launchpad.net/gcc-arm-embedded
+https://launchpad.net/~terry.guo/+archive/ubuntu/gcc-arm-embedded
 
 ```
 $ make -f Makefile.mbed