diff --git a/crates/oxc_isolated_declarations/src/signatures.rs b/crates/oxc_isolated_declarations/src/signatures.rs
index bb3a29a36f85e..54af9ea94107c 100644
--- a/crates/oxc_isolated_declarations/src/signatures.rs
+++ b/crates/oxc_isolated_declarations/src/signatures.rs
@@ -30,12 +30,12 @@ impl<'a> IsolatedDeclarations<'a> {
                         };
 
                         let entry = method_annotations.entry(name).or_default();
-                        entry.0 |= first_param.pattern.type_annotation.is_some();
+                        entry.0 |= first_param.pattern.type_annotation.is_none();
                         entry.1 = Some(&mut first_param.pattern.type_annotation);
                     }
                     TSMethodSignatureKind::Get => {
                         let entry = method_annotations.entry(name).or_default();
-                        entry.0 |= method.return_type.is_some();
+                        entry.0 |= method.return_type.is_none();
                         entry.2 = Some(&mut method.return_type);
                     }
                 };
diff --git a/crates/oxc_isolated_declarations/tests/fixtures/signatures.ts b/crates/oxc_isolated_declarations/tests/fixtures/signatures.ts
index 57efd21518f3d..aa7c76012ef7a 100644
--- a/crates/oxc_isolated_declarations/tests/fixtures/signatures.ts
+++ b/crates/oxc_isolated_declarations/tests/fixtures/signatures.ts
@@ -11,3 +11,10 @@ export interface I {
   set value(_);
   get value(): string;
 }
+
+
+// Do nothing
+export interface Ref<T = any, S = T> {
+  get value(): T
+  set value(_: S)
+}
\ No newline at end of file
diff --git a/crates/oxc_isolated_declarations/tests/snapshots/signatures.snap b/crates/oxc_isolated_declarations/tests/snapshots/signatures.snap
index 757b8cc6a6e74..dee8df0d152a6 100644
--- a/crates/oxc_isolated_declarations/tests/snapshots/signatures.snap
+++ b/crates/oxc_isolated_declarations/tests/snapshots/signatures.snap
@@ -23,3 +23,10 @@ export interface I {
 	set value(_: string);
 	get value(): string;
 }
+export interface Ref<
+	T = any,
+	S = T
+> {
+	get value(): T;
+	set value(_: S);
+}