diff --git a/highlighters/main/main-highlighter.zsh b/highlighters/main/main-highlighter.zsh
index e97b8b8..9ac15e9 100644
--- a/highlighters/main/main-highlighter.zsh
+++ b/highlighters/main/main-highlighter.zsh
@@ -662,12 +662,9 @@ _zsh_highlight_main_highlighter_highlight_list()
           next_word+=':start:'
           next_word+=':sudo_opt:'
         elif [[ $arg == '-'* ]]; then
-          # Unknown flag
+          # Unknown flag.  We don't know whether it takes an argument or not,
+          # so we don't modify $next_word.
           this_word=':sudo_opt:'
-          next_word+=':start:'
-          next_word+=':sudo_opt:'
-          _zsh_highlight_main_add_region_highlight $start_pos $end_pos unknown-token
-          continue
         else
           # Not an option flag; nothing to do.  (If the command line is
           # syntactically valid, ${this_word//:sudo_opt:/} should be
diff --git a/highlighters/main/test-data/precommand-unknown-option.zsh b/highlighters/main/test-data/precommand-unknown-option.zsh
index 1fba1b9..cd94233 100644
--- a/highlighters/main/test-data/precommand-unknown-option.zsh
+++ b/highlighters/main/test-data/precommand-unknown-option.zsh
@@ -38,6 +38,6 @@ expected_region_highlight=(
   '10 11 command' # ls
   '12 12 commandseparator' # ;
   '14 17 precommand' # sudo
-  '19 20 unknown-token' # -x
-  '22 23 command' # ls
+  '19 20 single-hyphen-option' # -x
+  '22 23 default' # ls
 )
diff --git a/highlighters/main/test-data/sudo-longopt.zsh b/highlighters/main/test-data/sudo-longopt.zsh
index 8c39142..7a2ea9d 100644
--- a/highlighters/main/test-data/sudo-longopt.zsh
+++ b/highlighters/main/test-data/sudo-longopt.zsh
@@ -32,6 +32,6 @@ BUFFER='sudo --askpass ls'
 
 expected_region_highlight=(
   '1 4 precommand' # sudo
-  '6 14 double-hyphen-option "issues #641 and #658"' # --askpass
-  '16 17 default "issues #641 and #658"' # ls (we don't know whether --askpass takes an argument)
+  '6 14 double-hyphen-option' # --askpass
+  '16 17 default' # ls (we don't know whether --askpass takes an argument)
 )