diff --git a/lib/productions/default.js b/lib/productions/default.js
new file mode 100644
index 00000000..f977b2ca
--- /dev/null
+++ b/lib/productions/default.js
@@ -0,0 +1,36 @@
+import { Base } from "./base";
+import { const_data, const_value } from "./helpers";
+
+export class Default extends Base {
+  /**
+   * @param {import("../tokeniser").Tokeniser} tokeniser
+   */
+  static parse(tokeniser) {
+    const assign = tokeniser.consume("=");
+    if (!assign) {
+      return null;
+    }
+    const def = const_value(tokeniser) || tokeniser.consume("string", "null", "[") || tokeniser.error("No value for default");
+    const expression = [def];
+    if (def.type === "[") {
+      const close = tokeniser.consume("]") || error("Default sequence value must be empty");
+      expression.push(close);
+    }
+    return new Default({ source: tokeniser.source, tokens: { assign }, expression });
+  }
+
+  constructor({ source, tokens, expression }) {
+    super({ source, tokens });
+    Object.defineProperty(this, "expression", { value: expression });
+  }
+
+  get type() {
+    return const_data(this.expression[0]).type;
+  }
+  get value() {
+    return const_data(this.expression[0]).value;
+  }
+  get negative() {
+    return const_data(this.expression[0]).negative;
+  }
+}
diff --git a/lib/productions/helpers.js b/lib/productions/helpers.js
index 14c16265..31e117b1 100644
--- a/lib/productions/helpers.js
+++ b/lib/productions/helpers.js
@@ -1,3 +1,6 @@
+/**
+ * @param {string} identifier 
+ */
 export function unescape(identifier) {
   return identifier.startsWith('_') ? identifier.slice(1) : identifier;
 }
@@ -31,3 +34,35 @@ export function list(tokeniser, { parser, allowDangler, listName = "list" }) {
   }
   return items;
 }
+
+/**
+ * @param {import("../tokeniser").Tokeniser} tokeniser
+ */
+export function const_value(tokeniser) {
+  return tokeniser.consume("true", "false", "Infinity", "-Infinity", "NaN", "decimal", "integer");
+}
+
+/**
+ * @param {object} token
+ * @param {string} token.type
+ * @param {string} token.value
+ */
+export function const_data({ type, value }) {
+  switch (type) {
+    case "true":
+    case "false":
+      return { type: "boolean", value: type === "true" };
+    case "Infinity":
+    case "-Infinity":
+      return { type: "Infinity", negative: type.startsWith("-") };
+    case "[":
+      return { type: "sequence", value: [] };
+    case "decimal":
+    case "integer":
+        return { type: "number", value };
+    case "string":
+      return { type: "string", value: value.slice(1, -1) };
+    default:
+      return { type };
+  }
+}
diff --git a/lib/webidl2.js b/lib/webidl2.js
index db0e85e8..d4f69ab8 100644
--- a/lib/webidl2.js
+++ b/lib/webidl2.js
@@ -4,7 +4,8 @@ import { argumentNameKeywords, stringTypes, Tokeniser } from "./tokeniser.js";
 import { Base } from "./productions/base.js";
 import { Token } from "./productions/token.js";
 import { Includes } from "./productions/includes.js";
-import { list, unescape } from "./productions/helpers.js";
+import { const_data, const_value, list, unescape } from "./productions/helpers.js";
+import { Default } from "./productions/default.js";
 
 /**
  * @param {Tokeniser} tokeniser
@@ -62,30 +63,6 @@ function parseByTokens(tokeniser) {
     }
   }
 
-  function const_value() {
-    return consume("true", "false", "Infinity", "-Infinity", "NaN", DECIMAL, INT);
-  }
-
-  function const_data(token) {
-    switch (token.type) {
-      case "true":
-      case "false":
-        return { type: "boolean", value: token.type === "true" };
-      case "Infinity":
-      case "-Infinity":
-        return { type: "Infinity", negative: token.type.startsWith("-") };
-      case DECIMAL:
-      case INT:
-        return { type: "number", value: token.value };
-      case "[":
-        return { type: "sequence", value: [] };
-      case STR:
-        return { type: STR, value: token.value.slice(1, -1) };
-      default:
-        return { type: token.type };
-    }
-  }
-
   function type_suffix(obj) {
     const nullable = consume("?");
     if (nullable) {
@@ -243,7 +220,7 @@ function parseByTokens(tokeniser) {
       if (!tokens.name) {
         return unconsume(start_position);
       }
-      ret.default = tokens.optional ? Default.parse() : null;
+      ret.default = tokens.optional ? Default.parse(tokeniser) : null;
       return ret;
     }
 
@@ -357,37 +334,6 @@ function parseByTokens(tokeniser) {
     }
   }
 
-  class Default extends Base {
-    static parse() {
-      const assign = consume("=");
-      if (!assign) {
-        return null;
-      }
-      const def = const_value() || consume(STR, "null", "[") || error("No value for default");
-      const expression = [def];
-      if (def.type === "[") {
-        const close = consume("]") || error("Default sequence value must be empty");
-        expression.push(close);
-      }
-      return new Default({ source, tokens: { assign }, expression });
-    }
-
-    constructor({ source, tokens, expression }) {
-      super({ source, tokens });
-      Object.defineProperty(this, "expression", { value: expression });
-    }
-
-    get type() {
-      return const_data(this.expression[0]).type;
-    }
-    get value() {
-      return const_data(this.expression[0]).value;
-    }
-    get negative() {
-      return const_data(this.expression[0]).negative;
-    }
-  }
-
   class Constant extends Base {
     static parse() {
       const tokens = {};
@@ -406,7 +352,7 @@ function parseByTokens(tokeniser) {
       idlType.type = "const-type";
       tokens.name = consume(ID) || error("No name for const");
       tokens.assign = consume("=") || error("No value assignment for const");
-      tokens.value = const_value() || error("No value for const");
+      tokens.value = const_value(tokeniser) || error("No value for const");
       tokens.termination = consume(";") || error("Unterminated const");
       const ret = new Constant({ source, tokens });
       ret.idlType = idlType;
@@ -800,7 +746,7 @@ function parseByTokens(tokeniser) {
       tokens.required = consume("required");
       ret.idlType = type_with_extended_attributes("dictionary-type") || error("No type for dictionary member");
       tokens.name = consume(ID) || error("No name for dictionary member");
-      ret.default = Default.parse();
+      ret.default = Default.parse(tokeniser);
       if (tokens.required && ret.default) error("Required member must not have a default");
       tokens.termination = consume(";") || error("Unterminated dictionary member");
       return ret;