diff --git a/src/compiler/emitter.ts b/src/compiler/emitter.ts
index a1207c9b892..ea06ec71268 100644
--- a/src/compiler/emitter.ts
+++ b/src/compiler/emitter.ts
@@ -411,7 +411,7 @@ namespace ts {
                     }
                 );
                 if (emitOnlyDtsFiles && declarationTransform.transformed[0].kind === SyntaxKind.SourceFile) {
-                    const sourceFile = declarationTransform.transformed[0] as SourceFile;
+                    const sourceFile = declarationTransform.transformed[0];
                     exportedModulesFromDeclarationEmit = sourceFile.exportedModulesFromDeclarationEmit;
                 }
             }