diff --git a/tools/profile.d-usrblackbox-test.sh b/tools/profile.d-usrblackbox-test.sh
new file mode 100755
index 0000000..df89f9b
--- /dev/null
+++ b/tools/profile.d-usrblackbox-test.sh
@@ -0,0 +1,44 @@
+#!/bin/sh
+
+# Test profile.d-usrblackbox.sh
+
+# Make sure profile.d-usrblackbox.sh works.
+
+# Test variations including /usr/blackbox/bin is not in the path, is
+# already there in the front, middle, or end, and tests if the path has :
+# in weird places (front, middle, or both).
+
+# To run the test:
+# bash  tools/profile.d-usrblackbox-test.sh | fgrep --color /usr/blackbox/bin
+# sh  profile.d-usrblackbox-test.sh | fgrep --color /usr/blackbox/bin
+
+# NOTE: profile.d-usrblackbox.sh is written to be so small that it fits as an "inline" file.
+# https://lwn.net/Articles/468678/
+# To remove the last newline in the file:
+#  perl -i -pe 'chomp if eof' profile.d-usrblackbox.sh
+
+for p in \
+  '/usr/local/bin:/bin:/usr/bin:/usr/local/sbin:/usr/sbin:/sbin'                     \
+  '/usr/blackbox/bin:/usr/local/bin:/bin:/usr/bin:/usr/local/sbin:/usr/sbin:/sbin'   \
+  '/usr/local/bin:/bin:/usr/blackbox/bin:/usr/bin:/usr/local/sbin:/usr/sbin:/sbin'   \
+  '/usr/local/bin:/bin:/usr/bin:/usr/local/sbin:/usr/sbin:/sbin:/usr/blackbox/bin'   \
+  '/Apple spaces/local/bin:/bin:/usr/bin:/usr/local/sbin:/usr/sbin:/sbin'   \
+  ; do
+
+  export PATH="$p"
+  . tools/profile.d-usrblackbox.sh
+  echo NEW: "$PATH"
+
+  export PATH=":$p"
+  . tools/profile.d-usrblackbox.sh
+  echo NEW: "$PATH"
+
+  export PATH="$p:"
+  . tools/profile.d-usrblackbox.sh
+  echo NEW: "$PATH"
+
+  export PATH=":$p:"
+  . tools/profile.d-usrblackbox.sh
+  echo NEW: "$PATH"
+
+done
diff --git a/tools/profile.d-usrblackbox.sh b/tools/profile.d-usrblackbox.sh
index 6c69b47..9a7f51b 100644
--- a/tools/profile.d-usrblackbox.sh
+++ b/tools/profile.d-usrblackbox.sh
@@ -1,2 +1,6 @@
-# Prepend to $PATH.
-pathmunge /usr/blackbox/bin
+x=/usr/blackbox/bin
+if type pathmunge >/dev/null 2>&1;then
+pathmunge $x
+elif ! grep -sqF :$x:<<<":$PATH:";then
+PATH="$x:$PATH"
+fi
\ No newline at end of file