diff --git a/app/services/word_watcher.rb b/app/services/word_watcher.rb
index 5dbf7a732d1..b9b48761ae3 100644
--- a/app/services/word_watcher.rb
+++ b/app/services/word_watcher.rb
@@ -15,14 +15,22 @@ class WordWatcher
   def self.word_matcher_regexp(action)
     s = Discourse.cache.fetch(word_matcher_regexp_key(action), expires_in: 1.day) do
       words = words_for_action(action)
-      words.empty? ? nil : '\b(' + words.map { |w| word_to_regexp(w) }.join('|'.freeze) + ')\b'
+      if words.empty?
+        nil
+      else
+        regexp = '(' + words.map { |w| word_to_regexp(w) }.join('|'.freeze) + ')'
+        SiteSetting.watched_words_regular_expressions? ? regexp : "(#{regexp})"
+      end
     end
-
     s.present? ? Regexp.new(s, Regexp::IGNORECASE) : nil
   end
 
   def self.word_to_regexp(word)
-    return word if SiteSetting.watched_words_regular_expressions?
+    if SiteSetting.watched_words_regular_expressions?
+      # Strip ruby regexp format if present, we're going to make the whole thing
+      # case insensitive anyway
+      return word.start_with?("(?-mix:") ? word[7..-2] : word
+    end
     Regexp.escape(word).gsub("\\*", '\S*')
   end
 
diff --git a/spec/services/word_watcher_spec.rb b/spec/services/word_watcher_spec.rb
index ba42f79bc6b..334446502c8 100644
--- a/spec/services/word_watcher_spec.rb
+++ b/spec/services/word_watcher_spec.rb
@@ -48,20 +48,36 @@ describe WordWatcher do
         expect(m[1]).to eq("acknowledge")
       end
 
-      it "supports regular expressions as a site setting" do
-        SiteSetting.watched_words_regular_expressions = true
-        Fabricate(
-          :watched_word,
-          word: "tro[uo]+t",
-          action: WatchedWord.actions[:require_approval]
-        )
-        m = WordWatcher.new("Evil Trout is cool").word_matches_for_action?(:require_approval)
-        expect(m[1]).to eq("Trout")
-        m = WordWatcher.new("Evil Troot is cool").word_matches_for_action?(:require_approval)
-        expect(m[1]).to eq("Troot")
-        m = WordWatcher.new("trooooooooot").word_matches_for_action?(:require_approval)
-        expect(m[1]).to eq("trooooooooot")
+      context "regular expressions" do
+        before do
+          SiteSetting.watched_words_regular_expressions = true
+        end
+
+        it "supports regular expressions on word boundaries" do
+          Fabricate(
+            :watched_word,
+            word: /\btest\b/,
+            action: WatchedWord.actions[:block]
+          )
+          m = WordWatcher.new("this is not a test.").word_matches_for_action?(:block)
+          expect(m[1]).to eq("test")
+        end
+
+        it "supports regular expressions as a site setting" do
+          Fabricate(
+            :watched_word,
+            word: /tro[uo]+t/,
+            action: WatchedWord.actions[:require_approval]
+          )
+          m = WordWatcher.new("Evil Trout is cool").word_matches_for_action?(:require_approval)
+          expect(m[1]).to eq("Trout")
+          m = WordWatcher.new("Evil Troot is cool").word_matches_for_action?(:require_approval)
+          expect(m[1]).to eq("Troot")
+          m = WordWatcher.new("trooooooooot").word_matches_for_action?(:require_approval)
+          expect(m[1]).to eq("trooooooooot")
+        end
       end
+
     end
   end