diff --git a/crates/oxc_isolated_declarations/src/lib.rs b/crates/oxc_isolated_declarations/src/lib.rs
index a5cb746f7be1a..1efa2c86c58ac 100644
--- a/crates/oxc_isolated_declarations/src/lib.rs
+++ b/crates/oxc_isolated_declarations/src/lib.rs
@@ -425,8 +425,18 @@ impl<'a> IsolatedDeclarations<'a> {
     ) -> FxHashMap<&'a str, FxHashSet<Atom>> {
         let mut assignable_properties_for_namespace = FxHashMap::<&str, FxHashSet<Atom>>::default();
         for stmt in stmts {
-            let Statement::ExportNamedDeclaration(decl) = stmt else { continue };
-            let Some(Declaration::TSModuleDeclaration(decl)) = &decl.declaration else { continue };
+            let decl = match stmt {
+                Statement::ExportNamedDeclaration(decl) => {
+                    if let Some(Declaration::TSModuleDeclaration(decl)) = &decl.declaration {
+                        decl
+                    } else {
+                        continue;
+                    }
+                }
+                Statement::TSModuleDeclaration(decl) => decl,
+                _ => continue,
+            };
+
             if decl.kind != TSModuleDeclarationKind::Namespace {
                 continue;
             }
diff --git a/crates/oxc_isolated_declarations/tests/fixtures/expando-function.ts b/crates/oxc_isolated_declarations/tests/fixtures/expando-function.ts
index 6856fbe2c75ab..c36a527cd1b1d 100644
--- a/crates/oxc_isolated_declarations/tests/fixtures/expando-function.ts
+++ b/crates/oxc_isolated_declarations/tests/fixtures/expando-function.ts
@@ -16,14 +16,19 @@ export namespace foo {
   export let baz = 100;
 }
 
-// namespace must be exported
-namespace foo {
-  export let bar = 42;
-}
-
 foo.bar = 42;
 foo.baz = 100;
 
 // unexported
 const zoo = (): void => {}
-zoo.toString = () => {}
\ No newline at end of file
+zoo.toString = () => {}
+
+function qux(): void {}
+
+namespace qux {
+  export let woo = 42;
+}
+
+qux.woo = 42;
+
+export default qux;
\ No newline at end of file
diff --git a/crates/oxc_isolated_declarations/tests/snapshots/expando-function.snap b/crates/oxc_isolated_declarations/tests/snapshots/expando-function.snap
index fe3405c670e92..7bd2565b320e0 100644
--- a/crates/oxc_isolated_declarations/tests/snapshots/expando-function.snap
+++ b/crates/oxc_isolated_declarations/tests/snapshots/expando-function.snap
@@ -12,6 +12,11 @@ export declare namespace NS {
 export declare namespace foo {
 	export let baz: number;
 }
+declare function qux(): void;
+declare namespace qux {
+	export let woo: number;
+}
+export default qux;
 
 
 ==================== Errors ====================
@@ -49,9 +54,9 @@ export declare namespace foo {
   x TS9023: Assigning properties to functions without declaring them is not
   | supported with --isolatedDeclarations. Add an explicit declaration for the
   | properties assigned to this function.
-    ,-[24:1]
- 23 | 
- 24 | foo.bar = 42;
+    ,-[19:1]
+ 18 | 
+ 19 | foo.bar = 42;
     : ^^^^^^^
- 25 | foo.baz = 100;
+ 20 | foo.baz = 100;
     `----