diff --git a/Makefile.in b/Makefile.in
index 9b52b6471..96119fa8e 100644
--- a/Makefile.in
+++ b/Makefile.in
@@ -79,7 +79,7 @@ ifeq ($(DESTDIR),)
                 echo "Not updating home directory location for user \"${RUNUSR}\" (not root)" ; \
             fi ; \
         fi ; \
-        if test `sw_vers -productVersion | /usr/bin/awk -F . '{print $$2}'` -eq 4 -a `id -u` -eq 0; then \
+        if test "@OS_MAJOR@" -eq 8 -a `id -u` -eq 0; then \
             GID=`${DSCL} -q . -read "/Groups/${RUNUSR}" PrimaryGroupID | /usr/bin/awk '{print $$2}'` ; \
             if test "`${DSCL} -q . -read "/Users/${RUNUSR}" PrimaryGroupID 2>/dev/null | /usr/bin/awk '{print $$2}'`" != "$$GID"; then \
                 echo "Fixing PrimaryGroupID for user \"${RUNUSR}\"" ; \
diff --git a/portmgr/dmg/postflight.in b/portmgr/dmg/postflight.in
index 7d2a49979..7232a979d 100755
--- a/portmgr/dmg/postflight.in
+++ b/portmgr/dmg/postflight.in
@@ -43,6 +43,7 @@ SBINPATH=${PREFIX}/sbin
 CONFIGPATH=${PREFIX}/etc/macports
 MANPAGES=${PREFIX}/share/man
 DSCL=/usr/bin/dscl
+OS_MAJOR=$(uname -r | cut -d . -f 1)
 RUNUSR=macports
 TCLSH="@TCLSH@"
 TCL_PACKAGE_PATH="@TCL_PACKAGE_PATH@"
@@ -182,7 +183,7 @@ function create_run_user {
         ${DSCL} -q . -create "/Users/${RUNUSR}" NFSHomeDirectory "${PREFIX}/var/macports/home"
         ${DSCL} -q . -create "/Users/${RUNUSR}" UserShell /usr/bin/false
     fi
-    if [[ $(sw_vers -productVersion | /usr/bin/awk -F . '{print $2}') -eq 4 ]]; then
+    if [[ "${OS_MAJOR}" -eq 8 ]]; then
         GID=$(${DSCL} -q . -read "/Groups/${RUNUSR}" PrimaryGroupID | /usr/bin/awk '{print $2}')
         if [[ "$(${DSCL} -q . -read "/Users/${RUNUSR}" PrimaryGroupID 2>/dev/null | /usr/bin/awk '{print $2}')" != "$GID" ]]; then
             echo "Fixing PrimaryGroupID for user \"${RUNUSR}\""
@@ -279,7 +280,7 @@ if /usr/bin/su "${USER}" -l -c "/usr/bin/printenv MANPATH" > /dev/null; then
 fi
 
 # Adding a DISPLAY variable only if we're running on Tiger or less and if it doesn't already exist:
-if (($(sw_vers -productVersion | awk -F . '{print $2}') >= 5)) || /usr/bin/su "${USER}" -l -c "/usr/bin/printenv DISPLAY" > /dev/null > /dev/null; then
+if [[ "${OS_MAJOR}" -ge 9 ]] || /usr/bin/su "${USER}" -l -c "/usr/bin/printenv DISPLAY" > /dev/null; then
     echo "Your shell already has the right DISPLAY environment variable for use with MacPorts!"
 else
     write_setting DISPLAY ":0"