diff --git a/changelogs/unreleased/update-issue-closing-pattern.yml b/changelogs/unreleased/update-issue-closing-pattern.yml
new file mode 100644
index 00000000000..95488adf449
--- /dev/null
+++ b/changelogs/unreleased/update-issue-closing-pattern.yml
@@ -0,0 +1,5 @@
+---
+title: Update issue closing pattern
+merge_request: 20554
+author: George Tsiolis
+type: changed
diff --git a/config/initializers/1_settings.rb b/config/initializers/1_settings.rb
index 693a2934a1b..4b9cc59ec45 100644
--- a/config/initializers/1_settings.rb
+++ b/config/initializers/1_settings.rb
@@ -135,7 +135,7 @@ Settings.gitlab['signup_enabled'] ||= true if Settings.gitlab['signup_enabled'].
 Settings.gitlab['signin_enabled'] ||= true if Settings.gitlab['signin_enabled'].nil?
 Settings.gitlab['restricted_visibility_levels'] = Settings.__send__(:verify_constant_array, Gitlab::VisibilityLevel, Settings.gitlab['restricted_visibility_levels'], [])
 Settings.gitlab['username_changing_enabled'] = true if Settings.gitlab['username_changing_enabled'].nil?
-Settings.gitlab['issue_closing_pattern'] = '((?:[Cc]los(?:e[sd]?|ing)|[Ff]ix(?:e[sd]|ing)?|[Rr]esolv(?:e[sd]?|ing)|[Ii]mplement(?:s|ed|ing)?)(:?) +(?:(?:issues? +)?%{issue_ref}(?:(?: *,? +and +| *, *)?)|([A-Z][A-Z0-9_]+-\d+))+)' if Settings.gitlab['issue_closing_pattern'].nil?
+Settings.gitlab['issue_closing_pattern'] = '((?:[Cc]los(?:e[sd]?|ing)|[Ff]ix(?:e[sd]|ing)?|[Rr]esolv(?:e[sd]?|ing)|[Ii]mplement(?:s|ed|ing)?)(:?) +(?:(?:issues? +)?%{issue_ref}(?:(?: *,? +and +| *,? *)?)|([A-Z][A-Z0-9_]+-\d+))+)' if Settings.gitlab['issue_closing_pattern'].nil?
 Settings.gitlab['default_projects_features'] ||= {}
 Settings.gitlab['webhook_timeout'] ||= 10
 Settings.gitlab['max_attachment_size'] ||= 10
diff --git a/spec/lib/gitlab/closing_issue_extractor_spec.rb b/spec/lib/gitlab/closing_issue_extractor_spec.rb
index 3a0688b7cbb..1f35d1e4880 100644
--- a/spec/lib/gitlab/closing_issue_extractor_spec.rb
+++ b/spec/lib/gitlab/closing_issue_extractor_spec.rb
@@ -379,6 +379,20 @@ describe Gitlab::ClosingIssueExtractor do
             .to match_array([issue, other_issue, third_issue])
       end
 
+      it 'allows non-comma-separated issue numbers in single line message' do
+        message = "Closes #{reference} #{reference2} #{reference3}"
+
+        expect(subject.closed_by_message(message))
+            .to match_array([issue, other_issue, third_issue])
+      end
+
+      it 'allows mixed comma-separated and non-comma-separated issue numbers in single line message' do
+        message = "Closes #{reference}, #{reference2} and #{reference3}"
+
+        expect(subject.closed_by_message(message))
+            .to match_array([issue, other_issue, third_issue])
+      end
+
       it 'fetches issues in multi-line message' do
         message = "Awesome commit (closes #{reference})\nAlso fixes #{reference2}"