diff --git a/src/internal.ts b/src/internal.ts
index c866253e8..ba1334864 100644
--- a/src/internal.ts
+++ b/src/internal.ts
@@ -8,14 +8,20 @@ import swc from "../lib/wasm.js";
 const DEFAULT_OPTIONS = {
 	mode: "strip-only",
 	deprecatedTsModuleAsError: true,
-	// default transform will only work when mode is "transform"
+} satisfies Options;
+
+// swc only reads `transform` in "transform" mode, so these defaults are kept
+// out of strip-only calls to avoid deserializing them on every call.
+const DEFAULT_TRANSFORM_OPTIONS = {
+	mode: "transform",
+	deprecatedTsModuleAsError: true,
 	transform: {
 		verbatimModuleSyntax: true,
 		nativeClassProperties: true,
 		noEmptyExport: true,
 		importNotUsedAsValues: "preserve",
 	},
-} as Options;
+} satisfies Options;
 
 export function transformSync(
 	source: string,
@@ -23,10 +29,9 @@ export function transformSync(
 ): TransformOutput {
 	// Ensure that the source code is a string
 	const input = `${source ?? ""}`;
-	return swc.transformSync(input, {
-		...DEFAULT_OPTIONS,
-		...options,
-	});
+	const defaults =
+		options?.mode === "transform" ? DEFAULT_TRANSFORM_OPTIONS : DEFAULT_OPTIONS;
+	return swc.transformSync(input, { ...defaults, ...options });
 }
 
 export function transformModuleSyntax(