diff --git a/implementations/javascript/packages/core/src/bytes.ts b/implementations/javascript/packages/core/src/bytes.ts
index c53c8e4..89fd2a1 100644
--- a/implementations/javascript/packages/core/src/bytes.ts
+++ b/implementations/javascript/packages/core/src/bytes.ts
@@ -172,11 +172,11 @@ export function hexDigit(n: number): string {
     return '0123456789abcdef'[n];
 }
 
-export function unhexDigit(asciiCode: number) {
+export function unhexDigit(asciiCode: number, errorClass: {new(msg: string): Error} = Error) {
     if (asciiCode >= 48 && asciiCode <= 57) return asciiCode - 48;
     if (asciiCode >= 97 && asciiCode <= 102) return asciiCode - 97 + 10;
     if (asciiCode >= 65 && asciiCode <= 70) return asciiCode - 65 + 10;
-    throw new Error("Invalid hex digit: " + String.fromCharCode(asciiCode));
+    throw new errorClass("Invalid hex digit: " + String.fromCharCode(asciiCode));
 }
 
 export function underlying(b: Bytes | Uint8Array): Uint8Array {
diff --git a/implementations/javascript/packages/core/src/reader.ts b/implementations/javascript/packages/core/src/reader.ts
index 4c914d7..3eaa823 100644
--- a/implementations/javascript/packages/core/src/reader.ts
+++ b/implementations/javascript/packages/core/src/reader.ts
@@ -4,7 +4,7 @@ import type { Value } from './values';
 import { DecodeError, ShortPacket } from './codec';
 import { Dictionary, Set } from './dictionary';
 import { strip } from './strip';
-import { Bytes, underlying, unhexDigit } from './bytes';
+import { Bytes, unhexDigit } from './bytes';
 import { Decoder, DecoderState, neverEmbeddedTypeDecode } from './decoder';
 import { Record } from './record';
 import { Annotated, newPosition, Position, updatePosition } from './annotated';
@@ -106,16 +106,16 @@ export class ReaderState {
     }
 
     readHex2(): number {
-        const x1 = unhexDigit(this.nextcharcode());
-        const x2 = unhexDigit(this.nextcharcode());
+        const x1 = unhexDigit(this.nextcharcode(), DecodeError);
+        const x2 = unhexDigit(this.nextcharcode(), DecodeError);
         return (x1 << 4) | x2;
     }
 
     readHex4(): number {
-        const x1 = unhexDigit(this.nextcharcode());
-        const x2 = unhexDigit(this.nextcharcode());
-        const x3 = unhexDigit(this.nextcharcode());
-        const x4 = unhexDigit(this.nextcharcode());
+        const x1 = unhexDigit(this.nextcharcode(), DecodeError);
+        const x2 = unhexDigit(this.nextcharcode(), DecodeError);
+        const x3 = unhexDigit(this.nextcharcode(), DecodeError);
+        const x4 = unhexDigit(this.nextcharcode(), DecodeError);
         return (x1 << 12) | (x2 << 8) | (x3 << 4) | x4;
     }
 
@@ -346,7 +346,7 @@ export class Reader<T> {
                     switch (c) {
                         case 'f': return false;
                         case 't': return true;
-                        case '{': return this.seq(new Set<T>(), (v, s) => s.add(v), '}');
+                        case '{': return this.readSet();
                         case '"': return this.state.readLiteralBinary();
                         case 'x': switch (this.state.nextchar()) {
                             case '"': return this.state.readHexBinary();
@@ -411,6 +411,16 @@ export class Reader<T> {
                         },
                         '}');
     }
+
+    readSet(): Set<T> {
+        return this.seq(new Set<T>(),
+                        (v, acc) => {
+                            if (acc.has(v)) this.state.error(
+                                `Duplicate value in set: ${stringify(v)}`, this.state.pos);
+                            acc.add(v);
+                        },
+                        '}');
+    }
 }
 
 const BASE64: {[key: string]: number} = {};
diff --git a/implementations/javascript/packages/core/test/codec.test.ts b/implementations/javascript/packages/core/test/codec.test.ts
index bbf5130..046eced 100644
--- a/implementations/javascript/packages/core/test/codec.test.ts
+++ b/implementations/javascript/packages/core/test/codec.test.ts
@@ -19,6 +19,7 @@ import {
     embed,
     genericEmbeddedTypeDecode,
     genericEmbeddedTypeEncode,
+    parse,
 } from '../src/index';
 const { Tag } = Constants;
 import './test-utils';
@@ -321,9 +322,23 @@ describe('common test suite', () => {
                 });
                 break;
             case Symbol.for('ParseError'):
+                describe(tName, () => {
+                    it('should fail with DecodeError', () => {
+                        expect(() => parse(strip(t[0]) as string))
+                            .toThrowFilter(e =>
+                                DecodeError.isDecodeError(e) &&
+                                !ShortPacket.isShortPacket(e));
+                    });
+                });
+                break;
             case Symbol.for('ParseEOF'):
             case Symbol.for('ParseShort'):
-                /* Skipped for now, until we have an implementation of text syntax */
+                describe(tName, () => {
+                    it('should fail with ShortPacket', () => {
+                        expect(() => parse(strip(t[0]) as string))
+                            .toThrowFilter(e => ShortPacket.isShortPacket(e));
+                    });
+                });
                 break;
             default:{
                 const e = new Error(preserves`Unsupported test kind ${t}`);