diff --git a/lib/optparse.rb b/lib/optparse.rb
index 97178e2..65a2d1f 100644
--- a/lib/optparse.rb
+++ b/lib/optparse.rb
@@ -1049,7 +1049,9 @@ def compsys(to, name = File.basename($0)) # :nodoc:
     to << "#compdef #{name}\n"
     to << COMPSYS_HEADER
     visit(:compsys, {}, {}) {|o, d|
-      to << %Q[  "#{o}[#{d.gsub(/[\\\"\[\]]/, '\\\\\&')}]" \\\n]
+      # Escape what zsh would expand inside the double quotes ($ and `), as
+      # well as the characters _arguments treats specially.
+      to << %Q[  "#{o}[#{d.gsub(/[\\\"\[\]$`]/, '\\\\\&')}]" \\\n]
     }
     to << "  '*:file:_files' && return 0\n"
   end
diff --git a/test/optparse/test_zsh_completion.rb b/test/optparse/test_zsh_completion.rb
index 76f0a73..12f0a9c 100644
--- a/test/optparse/test_zsh_completion.rb
+++ b/test/optparse/test_zsh_completion.rb
@@ -18,4 +18,10 @@ def test_compsys
     assert_match(/\"--bar\[\]\"/, compsys)
     assert_match(/\"--for\[\]\"/, compsys)
   end
+
+  def test_compsys_escapes_shell_expansion
+    @opt.define("--price", "costs $HOME and `date`") {}
+    compsys = @opt.compsys("", "zshcompsys")
+    assert_include(compsys, %q["--price[costs \\$HOME and \\`date\\`]"])
+  end
 end