diff --git a/highlighters/main/main-highlighter.zsh b/highlighters/main/main-highlighter.zsh
index 6eb37d8..30bbba5 100755
--- a/highlighters/main/main-highlighter.zsh
+++ b/highlighters/main/main-highlighter.zsh
@@ -120,8 +120,8 @@ _zsh_highlight_main_highlighter()
       # words for arguments).
       local needle=$'[;\n]'
       integer offset=${${buf[start_pos+1,-1]}[(i)$needle]}
-      (( start_pos += offset ))
-      (( end_pos += offset ))
+      (( start_pos += offset - 1 ))
+      (( end_pos = start_pos + $#arg ))
     else
       ((start_pos+=${#buf[$start_pos+1,-1]}-${#${buf[$start_pos+1,-1]##([[:space:]]|\\[[:space:]])#}}))
       ((end_pos=$start_pos+${#arg}))
diff --git a/highlighters/main/test-data/commandseparator.zsh b/highlighters/main/test-data/commandseparator.zsh
new file mode 100644
index 0000000..9325d84
--- /dev/null
+++ b/highlighters/main/test-data/commandseparator.zsh
@@ -0,0 +1,38 @@
+#!/usr/bin/env zsh
+# -------------------------------------------------------------------------------------------------
+# 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
+# -------------------------------------------------------------------------------------------------
+
+ZSH_HIGHLIGHT_STYLES[commandseparator]=$unused_highlight
+
+BUFFER=':; pwd'
+
+expected_region_highlight=(
+  "2 2 $ZSH_HIGHLIGHT_STYLES[commandseparator]" # ;
+  "4 6 $ZSH_HIGHLIGHT_STYLES[builtin]" # pwd
+)
diff --git a/tests/test-highlighting.zsh b/tests/test-highlighting.zsh
index 2e5a20c..0cbf793 100755
--- a/tests/test-highlighting.zsh
+++ b/tests/test-highlighting.zsh
@@ -91,11 +91,16 @@ for data_file in ${0:h:h}/highlighters/$1/test-data/*.zsh; do
       for i in {1..${#region_highlight}}; do
         highlight_zone=${(z)region_highlight[$i]}
         integer start=$highlight_zone[1] end=$highlight_zone[2]
-        (( --end )) # region_highlight ranges are half-open
-        (( ++start, ++end )) # region_highlight is 0-indexed; expected_region_highlight is 1-indexed
-        for j in {$start..$end}; do
-          observed_result[$j]=$highlight_zone[3]
-        done
+        if (( start < end )) # region_highlight ranges are half-open
+        then
+          (( --end )) # convert to closed range, like expected_region_highlight
+          (( ++start, ++end )) # region_highlight is 0-indexed; expected_region_highlight is 1-indexed
+          for j in {$start..$end}; do
+            observed_result[$j]=$highlight_zone[3]
+          done
+        else
+          # noop range; ignore.
+        fi
       done
 
       # Then we compare the observed result with the expected one.