diff --git a/internal/compiler/program.go b/internal/compiler/program.go
index 88a43728268..ddf3023f147 100644
--- a/internal/compiler/program.go
+++ b/internal/compiler/program.go
@@ -343,6 +343,8 @@ func canReplaceFileInProgram(file1 *ast.SourceFile, file2 *ast.SourceFile) bool
 	return file2 != nil &&
 		file1.ParseOptions() == file2.ParseOptions() &&
 		file1.UsesUriStyleNodeCoreModules == file2.UsesUriStyleNodeCoreModules &&
+		(file1.ExternalModuleIndicator != nil) == (file2.ExternalModuleIndicator != nil) &&
+		(file1.CommonJSModuleIndicator != nil) == (file2.CommonJSModuleIndicator != nil) &&
 		slices.EqualFunc(file1.Imports(), file2.Imports(), equalModuleSpecifiers) &&
 		slices.EqualFunc(file1.ModuleAugmentations, file2.ModuleAugmentations, equalModuleAugmentationNames) &&
 		slices.Equal(file1.AmbientModuleNames, file2.AmbientModuleNames) &&
diff --git a/internal/fourslash/tests/importHelpersAfterScriptBecomesDecoratedModule_test.go b/internal/fourslash/tests/importHelpersAfterScriptBecomesDecoratedModule_test.go
new file mode 100644
index 00000000000..1928537f424
--- /dev/null
+++ b/internal/fourslash/tests/importHelpersAfterScriptBecomesDecoratedModule_test.go
@@ -0,0 +1,47 @@
+package fourslash_test
+
+import (
+	"testing"
+
+	"github.com/microsoft/typescript-go/internal/fourslash"
+	"github.com/microsoft/typescript-go/internal/testutil"
+)
+
+func TestImportHelpersAfterScriptBecomesDecoratedModule(t *testing.T) {
+	t.Parallel()
+	defer testutil.RecoverAndFail(t, "Panic on fourslash test")
+
+	const content = `// @Filename: /tsconfig.json
+{
+	"compilerOptions": {
+		"target": "es2015",
+		"module": "commonjs",
+		"experimentalDecorators": true,
+		"importHelpers": true
+	},
+	"files": ["foo.ts"]
+}
+
+// @Filename: /foo.ts
+declare function dec(value: Function): void;
+/*insert*/class C {}
+
+// @Filename: /node_modules/tslib/package.json
+{ "name": "tslib", "typings": "tslib.d.ts" }
+
+// @Filename: /node_modules/tslib/tslib.d.ts
+export declare function __decorate(...args: any[]): any;
+
+// @Filename: /node_modules/tslib/tslib.js
+exports.__decorate = function () {};
+`
+	f, done := fourslash.NewFourslash(t, nil /*capabilities*/, content)
+	defer done()
+
+	f.GoToFile(t, "/foo.ts")
+	f.VerifyNumberOfErrorsInCurrentFile(t, 0)
+	f.Replace(t, f.MarkerByName(t, "insert").Position, 0, `@dec
+export `)
+	// The second diagnostics request forces external helper resolution after the edit.
+	f.VerifyNumberOfErrorsInCurrentFile(t, 0)
+}