--- a/bootstrap.sh
+++ b/bootstrap.sh
@@ -53,7 +53,7 @@
 
 # Try to respect $TMPDIR.
 [ -"$TMPDIR"- = -""- ] &&
-  export TMPDIR=/tmp/cabal-$(echo $(od -XN4 -An /dev/random)) && mkdir $TMPDIR
+  export TMPDIR=/tmp/cabal-$(echo $(od -tx2 -N4 -An /dev/random | tr -cd [0-9a-f])) && mkdir $TMPDIR
 
 # Check for a C compiler, using user-set $CC, if any, first.
 for c in $CC gcc clang cc icc; do