diff --git a/src/compiler/checker.ts b/src/compiler/checker.ts
index 1e16d2cbf0d..c7513deba56 100644
--- a/src/compiler/checker.ts
+++ b/src/compiler/checker.ts
@@ -23503,6 +23503,15 @@ namespace ts {
         }
 
         function getTypeReferenceSerializationKind(typeName: EntityName, location?: Node): TypeReferenceSerializationKind {
+            // ensure both `typeName` and `location` are parse tree nodes.
+            typeName = getParseTreeNode(typeName, isEntityName);
+            if (!typeName) return TypeReferenceSerializationKind.Unknown;
+
+            if (location) {
+                location = getParseTreeNode(location);
+                if (!location) return TypeReferenceSerializationKind.Unknown;
+            }
+
             // Resolve the symbol as a value to ensure the type can be reached at runtime during emit.
             const valueSymbol = resolveEntityName(typeName, SymbolFlags.Value, /*ignoreErrors*/ true, /*dontResolveAlias*/ false, location);
 
diff --git a/src/compiler/transformers/ts.ts b/src/compiler/transformers/ts.ts
index 71a3c7dcb7a..692c758bc75 100644
--- a/src/compiler/transformers/ts.ts
+++ b/src/compiler/transformers/ts.ts
@@ -1947,7 +1947,7 @@ namespace ts {
                     const name = getMutableClone(<Identifier>node);
                     name.flags &= ~NodeFlags.Synthesized;
                     name.original = undefined;
-                    name.parent = currentScope;
+                    name.parent = getParseTreeNode(currentScope); // ensure the parent is set to a parse tree node.
                     if (useFallback) {
                         return createLogicalAnd(
                             createStrictInequality(
diff --git a/src/harness/unittests/customTransforms.ts b/src/harness/unittests/customTransforms.ts
index 4b05ebb9ea7..f47bdad5d58 100644
--- a/src/harness/unittests/customTransforms.ts
+++ b/src/harness/unittests/customTransforms.ts
@@ -3,12 +3,11 @@
 
 namespace ts {
     describe("customTransforms", () => {
-        function emitsCorrectly(name: string, sources: { file: string, text: string }[], customTransformers: CustomTransformers) {
+        function emitsCorrectly(name: string, sources: { file: string, text: string }[], customTransformers: CustomTransformers, options: CompilerOptions = {}) {
             it(name, () => {
                 const roots = sources.map(source => createSourceFile(source.file, source.text, ScriptTarget.ES2015));
                 const fileMap = arrayToMap(roots, file => file.fileName);
                 const outputs = createMap<string>();
-                const options: CompilerOptions = {};
                 const host: CompilerHost = {
                     getSourceFile: (fileName) => fileMap.get(fileName),
                     getDefaultLibFileName: () => "lib.d.ts",
@@ -82,5 +81,25 @@ namespace ts {
         emitsCorrectly("before", sources, { before: [before] });
         emitsCorrectly("after", sources, { after: [after] });
         emitsCorrectly("both", sources, { before: [before], after: [after] });
+
+        emitsCorrectly("before+decorators", [{
+            file: "source.ts",
+            text: `
+                declare const dec: any;
+                class B {}
+                @dec export class C { constructor(b: B) { } }
+                'change'
+            `
+        }], {before: [
+            context => node => visitNode(node, function visitor(node: Node): Node {
+                if (isStringLiteral(node) && node.text === "change") return createLiteral("changed");
+                return visitEachChild(node, visitor, context);
+            })
+        ]}, {
+            target: ScriptTarget.ES5,
+            module: ModuleKind.ES2015,
+            emitDecoratorMetadata: true,
+            experimentalDecorators: true
+         });
     });
 }
\ No newline at end of file
diff --git a/tests/baselines/reference/customTransforms/before+decorators.js b/tests/baselines/reference/customTransforms/before+decorators.js
new file mode 100644
index 00000000000..ef705f0c9d8
--- /dev/null
+++ b/tests/baselines/reference/customTransforms/before+decorators.js
@@ -0,0 +1,26 @@
+// [source.js]
+var __decorate = (this && this.__decorate) || function (decorators, target, key, desc) {
+    var c = arguments.length, r = c < 3 ? target : desc === null ? desc = Object.getOwnPropertyDescriptor(target, key) : desc, d;
+    if (typeof Reflect === "object" && typeof Reflect.decorate === "function") r = Reflect.decorate(decorators, target, key, desc);
+    else for (var i = decorators.length - 1; i >= 0; i--) if (d = decorators[i]) r = (c < 3 ? d(r) : c > 3 ? d(target, key, r) : d(target, key)) || r;
+    return c > 3 && r && Object.defineProperty(target, key, r), r;
+};
+var __metadata = (this && this.__metadata) || function (k, v) {
+    if (typeof Reflect === "object" && typeof Reflect.metadata === "function") return Reflect.metadata(k, v);
+};
+var B = /** @class */ (function () {
+    function B() {
+    }
+    return B;
+}());
+var C = /** @class */ (function () {
+    function C(b) {
+    }
+    C = __decorate([
+        dec,
+        __metadata("design:paramtypes", [B])
+    ], C);
+    return C;
+}());
+export { C };
+"changed";