diff --git a/changelog/fix_incorrect_autocorrect_for_style_single_line_methods.md b/changelog/fix_incorrect_autocorrect_for_style_single_line_methods.md
new file mode 100644
index 00000000000..5e6e09297b9
--- /dev/null
+++ b/changelog/fix_incorrect_autocorrect_for_style_single_line_methods.md
@@ -0,0 +1 @@
+* [#9926](https://github.com/rubocop/rubocop/pull/9926): Fix an incorrect auto-correct for `Style/SingleLineMethods` when method body is enclosed in parentheses. ([@koic][])
diff --git a/lib/rubocop/cop/style/mutable_constant.rb b/lib/rubocop/cop/style/mutable_constant.rb
index 1bb3bf3b886..e6e509a5d93 100644
--- a/lib/rubocop/cop/style/mutable_constant.rb
+++ b/lib/rubocop/cop/style/mutable_constant.rb
@@ -62,13 +62,12 @@ class MutableConstant < Base
 
         def on_casgn(node)
           _scope, _const_name, value = *node
-          on_assignment(value)
-        end
+          if value.nil? # This is only the case for `CONST += ...` or similarg66
+            parent = node.parent
+            return unless parent.or_asgn_type? # We only care about `CONST ||= ...`
 
-        def on_or_asgn(node)
-          lhs, value = *node
-
-          return unless lhs&.casgn_type?
+            value = parent.children.last
+          end
 
           on_assignment(value)
         end
@@ -119,14 +118,13 @@ def autocorrect(corrector, node)
         end
 
         def mutable_literal?(value)
-          return false if value.nil?
           return false if frozen_regexp_or_range_literals?(value)
 
           value.mutable_literal?
         end
 
         def immutable_literal?(node)
-          node.nil? || frozen_regexp_or_range_literals?(node) || node.immutable_literal?
+          frozen_regexp_or_range_literals?(node) || node.immutable_literal?
         end
 
         def frozen_string_literal?(node)
diff --git a/lib/rubocop/cop/style/single_line_methods.rb b/lib/rubocop/cop/style/single_line_methods.rb
index 098dd7c4d7f..5e0f2a9bf68 100644
--- a/lib/rubocop/cop/style/single_line_methods.rb
+++ b/lib/rubocop/cop/style/single_line_methods.rb
@@ -72,17 +72,15 @@ def correct_to_endless?(body_node)
         end
 
         def correct_to_multiline(corrector, node)
-          each_part(node.body) do |part|
-            LineBreakCorrector.break_line_before(
-              range: part, node: node, corrector: corrector,
-              configured_width: configured_indentation_width
-            )
+          if (body = node.body) && body.begin_type? && body.parenthesized_call?
+            break_line_before(corrector, node, body)
+          else
+            each_part(body) do |part|
+              break_line_before(corrector, node, part)
+            end
           end
 
-          LineBreakCorrector.break_line_before(
-            range: node.loc.end, node: node, corrector: corrector,
-            indent_steps: 0, configured_width: configured_indentation_width
-          )
+          break_line_before(corrector, node, node.loc.end, indent_steps: 0)
 
           move_comment(node, corrector)
         end
@@ -96,6 +94,13 @@ def correct_to_endless(corrector, node)
           corrector.replace(node, replacement)
         end
 
+        def break_line_before(corrector, node, range, indent_steps: 1)
+          LineBreakCorrector.break_line_before(
+            range: range, node: node, corrector: corrector,
+            configured_width: configured_indentation_width, indent_steps: indent_steps
+          )
+        end
+
         def each_part(body)
           return unless body
 
diff --git a/spec/rubocop/cop/style/single_line_methods_spec.rb b/spec/rubocop/cop/style/single_line_methods_spec.rb
index 96b4c57d7aa..de3899ef801 100644
--- a/spec/rubocop/cop/style/single_line_methods_spec.rb
+++ b/spec/rubocop/cop/style/single_line_methods_spec.rb
@@ -32,6 +32,19 @@ def @table.columns;#{trailing_whitespace}
     RUBY
   end
 
+  it 'registers an offense for a single-line method and method body is enclosed in parentheses' do
+    expect_offense(<<~RUBY)
+      def foo() (do_something) end
+      ^^^^^^^^^^^^^^^^^^^^^^^^^^^^ Avoid single-line method definitions.
+    RUBY
+
+    expect_correction(<<~RUBY)
+      def foo()#{trailing_whitespace}
+        (do_something)#{trailing_whitespace}
+      end
+    RUBY
+  end
+
   context 'when AllowIfMethodIsEmpty is disabled' do
     let(:cop_config) { { 'AllowIfMethodIsEmpty' => false } }