diff --git a/share/functions/psub.fish b/share/functions/psub.fish
index afed1788e..37d702ca0 100644
--- a/share/functions/psub.fish
+++ b/share/functions/psub.fish
@@ -51,25 +51,24 @@ function psub --description "Read from stdin into a file and output the filename
         return 1
     end
 
-    set -l TMPDIR $TMPDIR
-    if test -z "$TMPDIR[1]"
-        set TMPDIR /tmp
-    end
+    set -l tmpdir /tmp
+    set -q TMPDIR
+    and set tmpdir $TMPDIR
 
     if test use_fifo = 1
         # Write output to pipe. This needs to be done in the background so
         # that the command substitution exits without needing to wait for
         # all the commands to exit
-        set dirname (mktemp -d "$TMPDIR[1]"/.psub.XXXXXXXXXX)
+        set dirname (mktemp -d $tmpdir/.psub.XXXXXXXXXX)
         or return
         set filename $dirname/psub.fifo"$suffix"
         mkfifo $filename
         cat >$filename &
     else if test -z $suffix
-        set filename (mktemp "$TMPDIR[1]"/.psub.XXXXXXXXXX)
+        set filename (mktemp $tmpdir/.psub.XXXXXXXXXX)
         cat >$filename
     else
-        set dirname (mktemp -d "$TMPDIR[1]"/.psub.XXXXXXXXXX)
+        set dirname (mktemp -d $tmpdir/.psub.XXXXXXXXXX)
         set filename $dirname/psub"$suffix"
         cat >$filename
     end