diff --git a/sim/configure.in b/sim/configure.in
index a451bd0aa5..f15b1c76ec 100644
--- a/sim/configure.in
+++ b/sim/configure.in
@@ -21,6 +21,10 @@ else
 fi
 AC_SUBST(CC_FOR_BUILD)
 
+# The PowerPC simulator uses the GCC extension long long as well as
+# ANSI prototypes, so don't enable it for random host compilers
+# unless asked to.
+
 AC_ARG_ENABLE(sim-powerpc,
 [  --enable-sim-powerpc ],
 [case "${enableval}" in