diff --git a/changelog/fix_an_error_for_lint_shadowing_outer_local_variable.md b/changelog/fix_an_error_for_lint_shadowing_outer_local_variable.md
new file mode 100644
index 00000000000..20a8e407165
--- /dev/null
+++ b/changelog/fix_an_error_for_lint_shadowing_outer_local_variable.md
@@ -0,0 +1 @@
+* [#10899](https://github.com/rubocop/rubocop/issues/10899): Fix an error for `Lint/ShadowingOuterLocalVariable` when the same variable name as a block variable is used in return value assignment of `if`. ([@koic][])
diff --git a/lib/rubocop/cop/lint/shadowing_outer_local_variable.rb b/lib/rubocop/cop/lint/shadowing_outer_local_variable.rb
index a381f8e87a1..ff715d30c6e 100644
--- a/lib/rubocop/cop/lint/shadowing_outer_local_variable.rb
+++ b/lib/rubocop/cop/lint/shadowing_outer_local_variable.rb
@@ -69,6 +69,7 @@ def same_conditions_node_different_branch?(variable, outer_local_variable)
 
           outer_local_variable_node =
             find_conditional_node_from_ascendant(outer_local_variable.declaration_node)
+          return true unless outer_local_variable_node
 
           outer_local_variable_node.conditional? && variable_node == outer_local_variable_node
         end
diff --git a/spec/rubocop/cop/lint/shadowing_outer_local_variable_spec.rb b/spec/rubocop/cop/lint/shadowing_outer_local_variable_spec.rb
index 29f557ce6a8..0f1e2b3f408 100644
--- a/spec/rubocop/cop/lint/shadowing_outer_local_variable_spec.rb
+++ b/spec/rubocop/cop/lint/shadowing_outer_local_variable_spec.rb
@@ -251,6 +251,18 @@ def some_method
     end
   end
 
+  context 'when the same variable name as a block variable is used in return value assignment of `if`' do
+    it 'does not register an offense' do
+      expect_no_offenses(<<~RUBY)
+        def some_method
+          foo = if condition
+                  bar { |foo| baz(foo) }
+                end
+        end
+      RUBY
+    end
+  end
+
   context 'when multiple block arguments have same name "_"' do
     it 'does not register an offense' do
       expect_no_offenses(<<~RUBY)