diff --git a/releng/releng_printsize b/releng/releng_printsize
index 6011d360..3dd4462c 100755
--- a/releng/releng_printsize
+++ b/releng/releng_printsize
@@ -22,8 +22,7 @@ else
  mkdir "${GEN_DATA_DIR}"
 fi
 
-RELENG_GENISOIMAGE=/usr/bin/genisoimage
-RELENG_MKISOFS=/usr/bin/mkisofs
+#
 UPPER=40
 
 # All must be set at this point
@@ -43,7 +42,7 @@ printf "done.\n"
 
 printf "\n${SELF}: Performing several print size runs to neutralize possible disk cache impact.\n"
 
-#
+# run xorriso
 if [ -x ${RELENG_XORRISO} ]; then
   for run in 1 2 3; do
       printf "\n${SELF}: Running ${RELENG_XORRISO} -as mkisofs -quiet -print-size ${GEN_DATA_DIR}. Trial: ${run}.\n"
@@ -51,16 +50,18 @@ if [ -x ${RELENG_XORRISO} ]; then
   done
 fi
 
-#
-if [ -x ${RELENG_GENISOIMAGE} ]; then
+# try to run genisoimage
+if which genisoimage >/dev/null 2>&1; then
+  RELENG_GENISOIMAGE=`which genisoimage`
   for run in 1 2 3; do
       printf "\n${SELF}: Running ${RELENG_GENISOIMAGE} -quiet -print-size ${GEN_DATA_DIR}. Trial: ${run}.\n"
       time ${RELENG_GENISOIMAGE}         -quiet -print-size ${GEN_DATA_DIR}
   done
 fi
 
-#
-if [ -x ${RELENG_MKISOFS} ]; then
+# try to run mkisofs
+if which mkisofs >/dev/null 2>&1; then
+  RELENG_MKISOFS=`which mkisofs`
   for run in 1 2 3; do
       printf "\n${SELF}: Running ${RELENG_MKISOFS} -quiet -print-size ${GEN_DATA_DIR}. Trial: ${run}.\n"
       time ${RELENG_MKISOFS}             -quiet -print-size ${GEN_DATA_DIR}