diff --git a/configure.ac b/configure.ac
index 7a66f1c98a..651e82b212 100644
--- a/configure.ac
+++ b/configure.ac
@@ -879,10 +879,12 @@ AC_DEFINE_UNQUOTED(OMPI_OFFSET_DATATYPE, $MPI_OFFSET_DATATYPE, [MPI datatype cor
 # sysconf(), but does not have _SC_NPROCESSORS_ONLN.  Doh!
 
 AC_MSG_CHECKING([for _SC_NPROCESSORS_ONLN])
-AC_TRY_COMPILE([#include <unistd.h>],
-    [(void)sysconf(_SC_NPROCESSORS_ONLN);],
-[MSG=yes VALUE=1], [MSG=no VALUE=0])
-AC_DEFINE_UNQUOTED(OPAL_HAVE__SC_NPROCESSORS_ONLN, $VALUE,
+AC_COMPILE_IFELSE(AC_LANG_SOURCE([[#include <unistd.h>
+]],[[int i = _SN_NPROCESSORS_ONLN;]]),
+    [MSG=yes OMPI_HAVE__SC_NPROCESSORS_ONLN=1], 
+    [MSG=no OMPI_HAVE__SC_NPROCESSORS_ONLN=0])
+AC_DEFINE_UNQUOTED(OPAL_HAVE__SC_NPROCESSORS_ONLN, 
+    $OMPI_HAVE__SC_NPROCESSORS_ONLN,
     [Whether we have the _SC_NPROCESSORS_ONLN])
 AC_MSG_RESULT([$MSG])
 
diff --git a/opal/mca/paffinity/darwin/configure.m4 b/opal/mca/paffinity/darwin/configure.m4
index e985fa409f..ce7dbfd1fe 100644
--- a/opal/mca/paffinity/darwin/configure.m4
+++ b/opal/mca/paffinity/darwin/configure.m4
@@ -10,7 +10,7 @@
 #                         University of Stuttgart.  All rights reserved.
 # Copyright (c) 2004-2005 The Regents of the University of California.
 #                         All rights reserved.
-# Copyright (c) 2007      Cisco, Inc. All rights reserved.
+# Copyright (c) 2007-2008 Cisco, Inc. All rights reserved.
 # Copyright (c) 2008      Sun Microsystems, Inc. All rights reserved.
 # $COPYRIGHT$
 # 
@@ -22,18 +22,12 @@
 # MCA_paffinity_darwin_CONFIG([action-if-found], [action-if-not-found])
 # -----------------------------------------------------------
 AC_DEFUN([MCA_paffinity_darwin_CONFIG],[
+    OMPI_VAR_SCOPE_PUSH([happy])
     # check to see if we have <mach/mach_host.h>
     # as this is a Darwin-specific thing
     AC_CHECK_HEADER([mach/mach_host.h], [happy=yes], [happy=no])
 
-    if test "$happy" = "yes"; then
-      AC_MSG_RESULT([$happy ])
-    fi
-
-    if test "$happy" = "yes"; then
-       $1
-    else
-       $2
-    fi
+    AS_IF([test "$happy" = "yes"], [$1], [$2])
+    OMPI_VAR_SCOPE_POP
 ])dnl
 
diff --git a/opal/mca/paffinity/posix/configure.m4 b/opal/mca/paffinity/posix/configure.m4
index fe711797e1..dac5ac7305 100644
--- a/opal/mca/paffinity/posix/configure.m4
+++ b/opal/mca/paffinity/posix/configure.m4
@@ -10,7 +10,7 @@
 #                         University of Stuttgart.  All rights reserved.
 # Copyright (c) 2004-2005 The Regents of the University of California.
 #                         All rights reserved.
-# Copyright (c) 2007      Cisco, Inc. All rights reserved.
+# Copyright (c) 2007-2008 Cisco, Inc. All rights reserved.
 # Copyright (c) 2008      Sun Microsystems, Inc. All rights reserved.
 # $COPYRIGHT$
 # 
@@ -22,17 +22,18 @@
 # MCA_paffinity_posix_CONFIG([action-if-found], [action-if-not-found])
 # -----------------------------------------------------------
 AC_DEFUN([MCA_paffinity_posix_CONFIG],[
-    #check to see if we have <unistd.h>
+    OMPI_VAR_SCOPE_PUSH([happy])
+    # Check to see if we have <unistd.h>
     AC_CHECK_HEADER([unistd.h], [happy=yes], [happy=no])
 
-    if test "$happy" = "yes"; then
-      AC_MSG_RESULT([$happy ])
-    fi
+    # Check to see if we have _SC_NPROCESSORS_ONLN
+    AS_IF([test "$happy" = "yes"],
+          [AC_MSG_CHECKING([for _SC_NPROCESSORS_ONLN])
+           AS_IF([test "$OMPI_HAVE__SC_NPROCESSORS_ONLN" = "1"],
+                 [happy=yes], [happy=no])
+           AC_MSG_RESULT([(cached) $happy])])
 
-    if test "$happy" = "yes"; then
-       $1
-    else
-       $2
-    fi
+    AS_IF([test "$happy" = "yes"], [$1], [$2])
+    OMPI_VAR_SCOPE_POP
 ])dnl