diff --git a/config/c_get_alignment.m4 b/config/c_get_alignment.m4
index 27ff8dc8ca..362df864d6 100644
--- a/config/c_get_alignment.m4
+++ b/config/c_get_alignment.m4
@@ -11,7 +11,7 @@ dnl                         University of Stuttgart.  All rights reserved.
 dnl Copyright (c) 2004-2005 The Regents of the University of California.
 dnl                         All rights reserved.
 dnl Copyright (c) 2009      Sun Microsystems, Inc.  All rights reserved.
-dnl Copyright (c) 2014      Intel, Inc. All rights reserved.
+dnl Copyright (c) 2014-2015 Intel, Inc. All rights reserved.
 dnl $COPYRIGHT$
 dnl 
 dnl Additional copyrights may follow
@@ -23,6 +23,13 @@ dnl
 # ----------------------------------
 # Determine datatype alignment. 
 # First arg is type, 2nd arg is config var to define.
+# Now that we require C99 compilers, we include stdbool.h
+# in the alignment test so that we can find the definition
+# of "bool" when we test for its alignment. We might be able
+# to avoid this if we test for alignemtn of _Bool, but
+# since we use "bool" in the code, let's be safe and check
+# what we use. Yes, they should be the same - but "should" and
+# "are" frequently differ
 AC_DEFUN([OPAL_C_GET_ALIGNMENT],[
     AC_CACHE_CHECK([alignment of $1],
                    [AS_TR_SH([opal_cv_c_align_$1])],