diff --git a/include/crm/error.h b/include/crm/error.h
index 2a1750ca38..56c64ffe87 100644
--- a/include/crm/error.h
+++ b/include/crm/error.h
@@ -1,42 +1,48 @@
 /* 
  * Copyright (C) 2012 Andrew Beekhof <andrew@beekhof.net>
  * 
  * This program is free software; you can redistribute it and/or
  * modify it under the terms of the GNU General Public
  * License as published by the Free Software Foundation; either
  * version 2 of the License, or (at your option) any later version.
  * 
  * This software is distributed in the hope that it will be useful,
  * but WITHOUT ANY WARRANTY; without even the implied warranty of
  * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
  * General Public License for more details.
  * 
  * You should have received a copy of the GNU General Public
  * License along with this library; if not, write to the Free Software
  * Foundation, Inc., 51 Franklin St, Fifth Floor, Boston, MA  02110-1301  USA
  */
 #ifndef CRM_ERROR__H
 #  define CRM_ERROR__H
 #  include <crm_config.h>
 #  include <assert.h>
 
+/*
+  System error codes
+  - /usr/include/asm-generic/errno.h
+  - /usr/include/asm-generic/errno-base.h
+*/
+
 #  define CRM_ASSERT(expr) do {						\
 	if(__unlikely((expr) == FALSE)) {				\
 	    crm_abort(__FILE__, __PRETTY_FUNCTION__, __LINE__, #expr, TRUE, FALSE); \
 	}								\
     } while(0)
 
 #  define pcmk_ok                       0
-#  define PCMK_ERROR_OFFSET             900  /* Replacements on non-linux systems */ 
+#  define PCMK_ERROR_OFFSET             900  /* Replacements on non-linux systems, see include/portability.h */ 
 #  define PCMK_CUSTOM_OFFSET            1000 /* Purely custom codes */
 #  define pcmk_err_generic              1001
 #  define pcmk_err_no_quorum            1002
 #  define pcmk_err_dtd_validation       1003
 #  define pcmk_err_transform_failed     1004
 #  define pcmk_err_old_data             1005
 #  define pcmk_err_diff_failed          1006
 #  define pcmk_err_diff_resync          1007
 
 const char *pcmk_strerror(int rc);
 
 #endif