diff --git a/highlighters/main/main-highlighter.zsh b/highlighters/main/main-highlighter.zsh
index 061e2a4..a76e64f 100644
--- a/highlighters/main/main-highlighter.zsh
+++ b/highlighters/main/main-highlighter.zsh
@@ -706,7 +706,18 @@ _zsh_highlight_main_highlighter_highlight_list()
     if [[ $this_word == *':start:'* ]] && ! (( in_redirection )); then
       # Expand aliases.
       # An alias is ineligible for expansion while it's being expanded (see #652/#653).
-      _zsh_highlight_main__type "$arg" "$(( ! ${+seen_alias[$arg]} ))"
+      () {
+        # :sudo_opt: marks every word from a recognised precommand (sudo,
+        # env, nice, ...) up to and including its actual command word.  Those
+        # precommands spawn their target via execvp(3)-style lookup, which
+        # (unlike the shell's own PATH_DIRS option) never searches $path for
+        # a name containing a slash -- so PATH_DIRS must not be honoured
+        # while classifying this word, or e.g. "sudo foo/bar" gets
+        # highlighted as a valid command when sudo itself would fail to find
+        # it (issue #595).
+        [[ $this_word == *':sudo_opt:'* ]] && local -a options_to_set=( ${options_to_set:#PATH_DIRS} )
+        _zsh_highlight_main__type "$arg" "$(( ! ${+seen_alias[$arg]} ))"
+      }
       local res="$REPLY"
       if [[ $res == "alias" ]]; then
         # Mark insane aliases as unknown-token (cf. #263).
@@ -737,7 +748,10 @@ _zsh_highlight_main_highlighter_highlight_list()
         continue
       else
         _zsh_highlight_main_highlighter_expand_path $arg
-        _zsh_highlight_main__type "$REPLY" 0
+        () {
+          [[ $this_word == *':sudo_opt:'* ]] && local -a options_to_set=( ${options_to_set:#PATH_DIRS} )
+          _zsh_highlight_main__type "$REPLY" 0
+        }
         res="$REPLY"
       fi
     fi
diff --git a/highlighters/main/test-data/sudo-path_dirs.zsh b/highlighters/main/test-data/sudo-path_dirs.zsh
new file mode 100644
index 0000000..598bfae
--- /dev/null
+++ b/highlighters/main/test-data/sudo-path_dirs.zsh
@@ -0,0 +1,50 @@
+# -------------------------------------------------------------------------------------------------
+# Copyright (c) 2015 zsh-syntax-highlighting contributors
+# All rights reserved.
+#
+# Redistribution and use in source and binary forms, with or without modification, are permitted
+# provided that the following conditions are met:
+#
+#  * Redistributions of source code must retain the above copyright notice, this list of conditions
+#    and the following disclaimer.
+#  * Redistributions in binary form must reproduce the above copyright notice, this list of
+#    conditions and the following disclaimer in the documentation and/or other materials provided
+#    with the distribution.
+#  * Neither the name of the zsh-syntax-highlighting contributors nor the names of its contributors
+#    may be used to endorse or promote products derived from this software without specific prior
+#    written permission.
+#
+# THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS" AND ANY EXPRESS OR
+# IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND
+# FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT HOLDER OR
+# CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
+# DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
+# DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER
+# IN CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT
+# OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
+# -------------------------------------------------------------------------------------------------
+# -*- mode: zsh; sh-indentation: 2; indent-tabs-mode: nil; sh-basic-offset: 2; -*-
+# vim: ft=zsh sw=2 ts=2 et
+# -------------------------------------------------------------------------------------------------
+
+# sudo(8) resolves its target command via execvp(3)-style lookup, which never
+# searches $path for a name containing a slash -- unlike the shell's own
+# PATH_DIRS option (see option-path_dirs.zsh). So even though PATH_DIRS makes
+# 'bar/testing-issue-228' resolve to a real command when run directly, the
+# same word after 'sudo' should not, since sudo itself wouldn't find it (#595).
+if [[ $OSTYPE == msys ]]; then
+  skip_test='Cannot chmod +x in msys2'
+else
+  setopt PATH_DIRS
+  mkdir -p foo/bar
+  touch foo/bar/testing-issue-228
+  chmod  +x foo/bar/testing-issue-228
+  path+=( "$PWD"/foo )
+
+  BUFFER='sudo bar/testing-issue-228'
+
+  expected_region_highlight=(
+    "1 4 precommand" # sudo
+    "6 26 unknown-token" # bar/testing-issue-228 -- not found via sudo's own lookup
+  )
+fi