diff --git a/activesupport/CHANGELOG.md b/activesupport/CHANGELOG.md
index 37d23f12ab..b2206764b1 100644
--- a/activesupport/CHANGELOG.md
+++ b/activesupport/CHANGELOG.md
@@ -1,3 +1,7 @@
+*   Fix `ActiveSupport::Inflector.humanize(nil)` raising ``NoMethodError: undefined method `end_with?' for nil:NilClass``.
+
+    *James Robinson*
+
 *   Don't show secrets for `ActiveSupport::KeyGenerator#inspect`.
 
     Before:
diff --git a/activesupport/lib/active_support/inflector/methods.rb b/activesupport/lib/active_support/inflector/methods.rb
index 2247e02db1..9a8d77ff7f 100644
--- a/activesupport/lib/active_support/inflector/methods.rb
+++ b/activesupport/lib/active_support/inflector/methods.rb
@@ -139,7 +139,7 @@ def humanize(lower_case_and_underscored_word, capitalize: true, keep_id_suffix:
 
       result.tr!("_", " ")
       result.lstrip!
-      if !keep_id_suffix && lower_case_and_underscored_word.end_with?("_id")
+      if !keep_id_suffix && lower_case_and_underscored_word&.end_with?("_id")
         result.delete_suffix!(" id")
       end
 
diff --git a/activesupport/test/inflector_test.rb b/activesupport/test/inflector_test.rb
index ec60a0a207..b4b20eb630 100644
--- a/activesupport/test/inflector_test.rb
+++ b/activesupport/test/inflector_test.rb
@@ -380,6 +380,10 @@ def test_humanize
     end
   end
 
+  def test_humanize_nil
+    assert_equal("", ActiveSupport::Inflector.humanize(nil))
+  end
+
   def test_humanize_without_capitalize
     UnderscoreToHumanWithoutCapitalize.each do |underscore, human|
       assert_equal(human, ActiveSupport::Inflector.humanize(underscore, capitalize: false))