diff --git a/packages/babel-plugin-transform-typescript/src/namespace.ts b/packages/babel-plugin-transform-typescript/src/namespace.ts
index 74532eca9412..54ceaf940b2b 100644
--- a/packages/babel-plugin-transform-typescript/src/namespace.ts
+++ b/packages/babel-plugin-transform-typescript/src/namespace.ts
@@ -185,6 +185,13 @@ function handleNested(
       case "TSEnumDeclaration":
       case "FunctionDeclaration":
       case "ClassDeclaration": {
+        if (
+          subNode.declaration.type === "ClassDeclaration" &&
+          subNode.declaration.declare
+        ) {
+          continue;
+        }
+
         const itemName = subNode.declaration.id.name;
         names.add(itemName);
         namespaceTopLevel.splice(
diff --git a/packages/babel-plugin-transform-typescript/test/fixtures/namespace/declare-class/input.ts b/packages/babel-plugin-transform-typescript/test/fixtures/namespace/declare-class/input.ts
new file mode 100644
index 000000000000..ab6316e99249
--- /dev/null
+++ b/packages/babel-plugin-transform-typescript/test/fixtures/namespace/declare-class/input.ts
@@ -0,0 +1,4 @@
+export namespace A {
+  export declare class B {
+  }
+}
\ No newline at end of file
diff --git a/packages/babel-plugin-transform-typescript/test/fixtures/namespace/declare-class/output.mjs b/packages/babel-plugin-transform-typescript/test/fixtures/namespace/declare-class/output.mjs
new file mode 100644
index 000000000000..d4cc47055d31
--- /dev/null
+++ b/packages/babel-plugin-transform-typescript/test/fixtures/namespace/declare-class/output.mjs
@@ -0,0 +1,3 @@
+export let A;
+
+(function (_A) {})(A || (A = {}));