diff --git a/gcc/ChangeLog b/gcc/ChangeLog
index f6243ce294c..77a51c62778 100644
--- a/gcc/ChangeLog
+++ b/gcc/ChangeLog
@@ -6,6 +6,9 @@
 	(-Wvariadic-macros): Alphabetize.
 	(-fsched-stalled-insns-dep): Add missing 'f'.
 
+	* c-cppbuiltin.c (c_cpp_builtins): Add comment for flag_stack_protect
+	macros.
+
 2005-08-13  David Edelsohn  <edelsohn@gnu.org>
 
 	* config/rs6000/rs6000.h (EXTRA_CONSTRAINT): Add 'a' for indexed
diff --git a/gcc/c-cppbuiltin.c b/gcc/c-cppbuiltin.c
index 44c7a3797dd..9020e0b49f9 100644
--- a/gcc/c-cppbuiltin.c
+++ b/gcc/c-cppbuiltin.c
@@ -440,7 +440,9 @@ c_cpp_builtins (cpp_reader *pfile)
   if (targetm.handle_pragma_extern_prefix)
     cpp_define (pfile, "__PRAGMA_EXTERN_PREFIX");
 
-  /* Make the choice of the stack protector runtime visible to source code.  */
+  /* Make the choice of the stack protector runtime visible to source code.
+     The macro names and values here were chosen for compatibility with an
+     earlier implementation, i.e. ProPolice.  */
   if (flag_stack_protect == 2)
     cpp_define (pfile, "__SSP_ALL__=2");
   else if (flag_stack_protect == 1)