diff --git a/app/models/account.rb b/app/models/account.rb
index a25ebc4aa..17882db9a 100644
--- a/app/models/account.rb
+++ b/app/models/account.rb
@@ -66,7 +66,7 @@ class Account < ApplicationRecord
   BACKGROUND_REFRESH_INTERVAL = 1.week.freeze
 
   USERNAME_RE   = /[a-z0-9_]+([a-z0-9_.-]+[a-z0-9_]+)?/i
-  MENTION_RE    = %r{(?<![=/[:word:]])@((#{USERNAME_RE})(?:@[[:word:].-]+[[:word:]]+)?)}i
+  MENTION_RE    = %r{(?<![=/[:word:]])@((#{USERNAME_RE})(?:@[[:word:].-]+[[:word:]]+)?)}
   URL_PREFIX_RE = %r{\Ahttp(s?)://[^/]+}
   USERNAME_ONLY_RE = /\A#{USERNAME_RE}\z/i
 
diff --git a/app/models/tag.rb b/app/models/tag.rb
index c61079ba2..2d75aa2cc 100644
--- a/app/models/tag.rb
+++ b/app/models/tag.rb
@@ -35,7 +35,7 @@ class Tag < ApplicationRecord
   HASHTAG_LAST_SEQUENCE = '([[:word:]_]*[[:alpha:]][[:word:]_]*)'
   HASHTAG_NAME_PAT = "#{HASHTAG_FIRST_SEQUENCE}|#{HASHTAG_LAST_SEQUENCE}"
 
-  HASHTAG_RE = %r{(?<![=/)\p{Alnum}])#(#{HASHTAG_NAME_PAT})}i
+  HASHTAG_RE = %r{(?<![=/)\p{Alnum}])#(#{HASHTAG_NAME_PAT})}
   HASHTAG_NAME_RE = /\A(#{HASHTAG_NAME_PAT})\z/i
   HASHTAG_INVALID_CHARS_RE = /[^[:alnum:]#{HASHTAG_SEPARATORS}]/
 
diff --git a/spec/models/account_spec.rb b/spec/models/account_spec.rb
index fc7a43110..5fcbf4607 100644
--- a/spec/models/account_spec.rb
+++ b/spec/models/account_spec.rb
@@ -703,6 +703,14 @@ RSpec.describe Account do
     it 'does not match URL query string' do
       expect(subject.match('https://example.com/?x=@alice')).to be_nil
     end
+
+    it 'matches usernames immediately following the letter ß' do
+      expect(subject.match('Hello toß @alice from me')[1]).to eq 'alice'
+    end
+
+    it 'matches usernames containing uppercase characters' do
+      expect(subject.match('Hello to @aLice@Example.com from me')[1]).to eq 'aLice@Example.com'
+    end
   end
 
   describe 'validations' do
diff --git a/spec/models/tag_spec.rb b/spec/models/tag_spec.rb
index 26d0fa25f..529de3269 100644
--- a/spec/models/tag_spec.rb
+++ b/spec/models/tag_spec.rb
@@ -95,6 +95,14 @@ RSpec.describe Tag do
     it 'does not match purely-numeric hashtags' do
       expect(subject.match('hello #0123456')).to be_nil
     end
+
+    it 'matches hashtags immediately following the letter ß' do
+      expect(subject.match('Hello toß #ruby').to_s).to eq '#ruby'
+    end
+
+    it 'matches hashtags containing uppercase characters' do
+      expect(subject.match('Hello #rubyOnRails').to_s).to eq '#rubyOnRails'
+    end
   end
 
   describe '#to_param' do