diff --git a/etc/defaults/make.conf b/etc/defaults/make.conf
index b528c355c1f..0ce68625e5a 100644
--- a/etc/defaults/make.conf
+++ b/etc/defaults/make.conf
@@ -9,7 +9,13 @@
 # You have to find the things you can put here in the Makefiles and 
 # documentation of the source tree.
 #
-# One, and probably the most common, use could be:
+# CFLAGS controls the compiler settings used when compiling C code.
+# Note that optimisation settings above -O (-O2, ...) are not recommended
+# or supported for compiling the world or the kernel - please revert any
+# nonstandard optimisation settings to "-O" before submitting bug reports
+# to the developers.
+# Note also that at this time the -O2 setting is known to produce BROKEN
+# CODE on the Alpha platform.
 #
 #CFLAGS= -O -pipe
 #
diff --git a/share/examples/etc/make.conf b/share/examples/etc/make.conf
index b528c355c1f..0ce68625e5a 100644
--- a/share/examples/etc/make.conf
+++ b/share/examples/etc/make.conf
@@ -9,7 +9,13 @@
 # You have to find the things you can put here in the Makefiles and 
 # documentation of the source tree.
 #
-# One, and probably the most common, use could be:
+# CFLAGS controls the compiler settings used when compiling C code.
+# Note that optimisation settings above -O (-O2, ...) are not recommended
+# or supported for compiling the world or the kernel - please revert any
+# nonstandard optimisation settings to "-O" before submitting bug reports
+# to the developers.
+# Note also that at this time the -O2 setting is known to produce BROKEN
+# CODE on the Alpha platform.
 #
 #CFLAGS= -O -pipe
 #