diff --git a/app/javascript/src/javascripts/autocomplete.js.erb b/app/javascript/src/javascripts/autocomplete.js.erb
index 4899141c1..05361d383 100644
--- a/app/javascript/src/javascripts/autocomplete.js.erb
+++ b/app/javascript/src/javascripts/autocomplete.js.erb
@@ -10,8 +10,8 @@ Autocomplete.ORDER_METATAGS = <%= Tag::ORDER_METATAGS.to_json.html_safe %>;
 /* eslint-enable */
 
 Autocomplete.TAG_PREFIXES = "-|~|" + Object.keys(Autocomplete.TAG_CATEGORIES).map(category => category + ":").join("|");
-Autocomplete.TAG_PREFIXES_REGEX = new RegExp("^(" + Autocomplete.TAG_PREFIXES + ")(.*)$", "i");
-Autocomplete.METATAGS_REGEX = new RegExp("^(" + Autocomplete.METATAGS.join("|") + "):(.*)$", "i");
+Autocomplete.METATAGS_REGEX = Autocomplete.METATAGS.concat(Object.keys(Autocomplete.TAG_CATEGORIES)).join("|");
+Autocomplete.TERM_REGEX = new RegExp(`([-~]*)(?:(${Autocomplete.METATAGS_REGEX}):)?(\\S*)$`, "i");
 
 Autocomplete.initialize_all = function() {
   if (Utility.meta("enable-auto-complete") === "true") {
@@ -271,34 +271,14 @@ Autocomplete.normal_source = function(term, resp) {
 }
 
 Autocomplete.parse_query = function(text, caret) {
-  var operator = "";
-  var metatag = "";
-  var term = "";
+  let before_caret_text = text.substring(0, caret);
+  let match = before_caret_text.match(Autocomplete.TERM_REGEX);
 
-  var before_caret_text = text.substring(0, caret);
-  var match = before_caret_text.match(/\S+$/g);
-  if (match) {
-    term = match[0];
-  } else {
-    return {};
-  }
+  let operator = match[1];
+  let metatag = match[2] ? match[2].toLowerCase() : "tag";
+  let term = match[3];
 
-  match = term.match(/^([-~])(.*)$/);
-  if (match) {
-    operator = match[1];
-    term = match[2];
-  }
-
-  match = term.match(Autocomplete.TAG_PREFIXES_REGEX);
-  if (match) {
-    term = match[2];
-  }
-
-  match = term.match(Autocomplete.METATAGS_REGEX);
-  if (match) {
-    metatag = match[1].toLowerCase();
-    term = match[2];
-  } else {
+  if (metatag in Autocomplete.TAG_CATEGORIES) {
     metatag = "tag";
   }
 
diff --git a/test/application_system_test_case.rb b/test/application_system_test_case.rb
index 6faf93767..9ca42980a 100644
--- a/test/application_system_test_case.rb
+++ b/test/application_system_test_case.rb
@@ -2,5 +2,5 @@ require "test_helper"
 
 class ApplicationSystemTestCase < ActionDispatch::SystemTestCase
   include SystemTestHelper
-  driven_by :selenium, using: :firefox, screen_size: [1400, 1400]
+  driven_by :selenium, using: :headless_firefox, screen_size: [1400, 1400]
 end
diff --git a/test/system/autocomplete_test.rb b/test/system/autocomplete_test.rb
index 4326a1176..6877b33e9 100644
--- a/test/system/autocomplete_test.rb
+++ b/test/system/autocomplete_test.rb
@@ -30,6 +30,12 @@ class AutocompleteTest < ApplicationSystemTestCase
     assert_autocomplete_equals(values, text, id: "forum_post_body")
   end
 
+  def assert_inserted_completion(result, query, id: "tags")
+    autocomplete(id, query)
+    first("ul.ui-autocomplete li").click
+    assert_equal(result, find_field(id: id).value)
+  end
+
   context "Autocomplete" do
     context "for post searches" do
       should "work for static metatags" do
@@ -85,8 +91,6 @@ class AutocompleteTest < ApplicationSystemTestCase
         assert_search_autocomplete_equals(["bkub"], "char:bkub")
         assert_search_autocomplete_equals(["bkub"], "gen:bkub")
         assert_search_autocomplete_equals(["bkub"], "meta:bkub")
-        assert_search_autocomplete_equals(["bkub"], "-char:bkub")
-        assert_search_autocomplete_equals(["bkub"], "~char:bkub")
 
         assert_search_autocomplete_equals(["bkub"], "b*")
         assert_search_autocomplete_equals(["bkub"], "B*")
@@ -98,16 +102,38 @@ class AutocompleteTest < ApplicationSystemTestCase
         assert_search_autocomplete_equals([], "one two")
       end
 
+      should "correct invalid operator combinations" do
+        create(:tag, name: "bkub", post_count: 42)
+
+        assert_search_autocomplete_equals(["bkub"], "foo ---bkub")
+        assert_search_autocomplete_equals(["bkub"], "foo ~~~bkub")
+
+        assert_search_autocomplete_equals(["rating:safe"], "--rating:s")
+        assert_search_autocomplete_equals(["rating:safe"], "-~rating:s")
+        assert_search_autocomplete_equals(["rating:safe"], "~-rating:s")
+        assert_search_autocomplete_equals(["rating:safe"], "~~rating:s")
+        assert_search_autocomplete_equals(["rating:safe"], "---rating:s")
+        assert_search_autocomplete_equals(["rating:safe"], "~~~rating:s")
+      end
+
+      should "ignore invalid prefix + metatag combinations" do
+        assert_search_autocomplete_equals([], "char:rating:s")
+      end
+
       should "insert completions on click" do
         visit posts_path
 
-        autocomplete("tags", "rating:s")
-        first("ul.ui-autocomplete li").click
-        assert_equal("rating:safe ", find_field(id: "tags").value)
+        create(:tag, name: "bkub", post_count: 42)
+        assert_inserted_completion("bkub ", "b")
+        assert_inserted_completion("-bkub ", "-b")
+        assert_inserted_completion("~bkub ", "~b")
+        assert_inserted_completion("tag bkub ", "tag b")
+        assert_inserted_completion("tag char:bkub ", "tag char:b")
 
-        autocomplete("tags", "one two rating:s")
-        first("ul.ui-autocomplete li").click
-        assert_equal("one two rating:safe ", find_field(id: "tags").value)
+        assert_inserted_completion("rating:safe ", "rating:s")
+        assert_inserted_completion("-rating:safe ", "-rating:s")
+        assert_inserted_completion("-rating:safe ", "---rating:s")
+        assert_inserted_completion("tag rating:safe ", "tag rating:s")
       end
     end