diff --git a/app/models/dmail_filter.rb b/app/models/dmail_filter.rb
index ad5b16d24..6cd8f58f1 100644
--- a/app/models/dmail_filter.rb
+++ b/app/models/dmail_filter.rb
@@ -1,4 +1,6 @@
 class DmailFilter < ApplicationRecord
+  extend Memoist
+
   belongs_to :user
   validates_presence_of :user
   before_validation :initialize_user
@@ -18,6 +20,9 @@ class DmailFilter < ApplicationRecord
   end
 
   def regexp
-    @regexp ||= /\b#{Regexp.union(words.split(/[[:space:]]+/))}\b/
+    union = words.split(/[[:space:]]+/).map { |word| Regexp.escape(word) }.join("|")
+    /\b#{union}\b/i
   end
+
+  memoize :regexp
 end
diff --git a/test/unit/dmail_filter_test.rb b/test/unit/dmail_filter_test.rb
index 2c62ae506..c476ed6b5 100644
--- a/test/unit/dmail_filter_test.rb
+++ b/test/unit/dmail_filter_test.rb
@@ -28,6 +28,11 @@ class DmailFilterTest < ActiveSupport::TestCase
       create_dmail("okay", "banned")
       assert_equal(true, @receiver.dmails.last.is_read?)
     end
+
+    should "be case insensitive" do
+      create_dmail("Banned.", "okay")
+      assert_equal(true, @receiver.dmails.last.is_read?)
+    end
   end
 
   context "a dmail filter for a user name" do
@@ -40,4 +45,13 @@ class DmailFilterTest < ActiveSupport::TestCase
       assert_equal(true, @receiver.dmails.last.is_read?)
     end
   end
+
+  context "a dmail filter containing multiple words" do
+    should "filter dmails containing any of the words" do
+      @receiver.create_dmail_filter(words: "foo bar spam")
+      create_dmail("this is a test (not *SPAM*)", "hello world")
+
+      assert_equal(true, @receiver.dmails.last.is_read?)
+    end
+  end
 end