diff --git a/.gitignore b/.gitignore
index 772f6063..20bd5ece 100644
--- a/.gitignore
+++ b/.gitignore
@@ -2,3 +2,4 @@
 index.ids
 deploy_key
 index.html
+/node_modules/
diff --git a/.travis.yml b/.travis.yml
index dd244e65..0e777890 100644
--- a/.travis.yml
+++ b/.travis.yml
@@ -1,4 +1,6 @@
-language: generic
+language: node_js
+node_js:
+  - "node"
 
 script:
   - bash ./deploy.sh
diff --git a/check-grammar.js b/check-grammar.js
new file mode 100644
index 00000000..cbd9acc3
--- /dev/null
+++ b/check-grammar.js
@@ -0,0 +1,50 @@
+"use strict";
+const Grammar = require("syntax-cli").Grammar;
+const LLParsingTable = require("syntax-cli").LLParsingTable;
+const jsdom = require("jsdom");
+const fs = require("fs");
+
+function getRulesFromDOM(window) {
+    let rules = window.document.querySelectorAll("pre.grammar[id]");
+    return [].map.call(rules, pre => pre.textContent);
+}
+
+function processRules(rules) {
+    const REGEXP = /(\s*:\n\s*)|\b(integer|float|identifier|string|whitespace|comment|other)\b|(\s*\n\s*)|(ε)/g;
+    return rules.map(rule => {
+        return rule.trim().replace(REGEXP, m => {
+            if (/^(integer|float|identifier|string|whitespace|comment|other)$/.test(m)) {
+              return m.toUpperCase();
+            }
+            if (/:\n/.test(m)) { return "\n  : "; }
+            if (/\n/.test(m)) { return "\n  | "; }
+            if (/ε/.test(m)) { return "/* epsilon */"; }
+        }) + "\n  ;";
+    });
+}
+
+function toBNF(rules) {
+    return "\n%%\n\n" + processRules(rules).join("\n");
+}
+
+let path = process.argv[2];
+let html = fs.readFileSync(path, "utf8");
+let dom = new jsdom.JSDOM(html);
+let rules = getRulesFromDOM(dom.window);
+let bnf = toBNF(rules);
+let data = Grammar.dataFromString(bnf, "bnf");
+let grammar = Grammar.fromData(data, { mode: "LL1" });
+let table = new LLParsingTable({ grammar: grammar });
+let conflicts = table.getConflicts();
+if (table.hasConflicts()) {
+    console.log("The WebIDL grammar is NOT LL(1) due to the following conflicts:");
+    Object.keys(conflicts).forEach((nt, i) => {
+        let conflict = conflicts[nt];
+        let str = Object.keys(conflict).map(k => `       * ${k} (${ conflict[k] })`).join("\n");
+        console.log(`    ${i+1}. ${ nt }:\n${ str }`);
+    });
+    process.exit(1);
+} else {
+    console.log("The WebIDL grammar is LL(1).");
+    process.exit(0);
+}
diff --git a/deploy.sh b/deploy.sh
index 1d0fbc32..7e767dbe 100755
--- a/deploy.sh
+++ b/deploy.sh
@@ -6,6 +6,7 @@ TARGET_BRANCH="gh-pages"
 
 function doCompile {
   curl https://api.csswg.org/bikeshed/ -F file=@index.bs > out/index.html
+  node ./check-grammar.js ./out/index.html
 }
 
 # Pull requests and commits to other branches shouldn't try to deploy, just build to verify
diff --git a/index.bs b/index.bs
index 628de3cb..ffe995a5 100644
--- a/index.bs
+++ b/index.bs
@@ -1974,8 +1974,13 @@ The following extended attributes are applicable to operations:
 
 <pre class="grammar" id="prod-Argument">
     Argument :
-        ExtendedAttributeList "optional" TypeWithExtendedAttributes ArgumentName Default
-        ExtendedAttributeList Type Ellipsis ArgumentName
+        ExtendedAttributeList ArgumentRest
+</pre>
+
+<pre class="grammar" id="prod-ArgumentRest">
+    ArgumentRest :
+        "optional" TypeWithExtendedAttributes ArgumentName Default
+        Type Ellipsis ArgumentName
 </pre>
 
 <pre class="grammar" id="prod-ArgumentName">
@@ -4232,8 +4237,13 @@ No [=extended attributes=] are applicable to dictionaries.
 
 <pre class="grammar" id="prod-DictionaryMember">
     DictionaryMember :
-        ExtendedAttributeList "required" TypeWithExtendedAttributes identifier Default ";"
-        ExtendedAttributeList Type identifier Default ";"
+        ExtendedAttributeList DictionaryMemberRest
+</pre>
+
+<pre class="grammar" id="prod-DictionaryMemberRest">
+    DictionaryMemberRest :
+        "required" TypeWithExtendedAttributes identifier Default ";"
+        Type identifier Default ";"
 </pre>
 
 <pre class="grammar" id="prod-PartialDictionary">
@@ -5083,8 +5093,7 @@ type.
 
 <pre class="grammar" id="prod-TypeWithExtendedAttributes">
     TypeWithExtendedAttributes :
-        ExtendedAttributeList SingleType
-        ExtendedAttributeList UnionType Null
+        ExtendedAttributeList Type
 </pre>
 
 <pre class="grammar" id="prod-SingleType">
diff --git a/package.json b/package.json
new file mode 100644
index 00000000..854dafcb
--- /dev/null
+++ b/package.json
@@ -0,0 +1,8 @@
+{
+  "private": true,
+  "description": "Checks that the WebIDL grammar is LL(1)",
+  "devDependencies": {
+    "jsdom": "^11.3.0",
+    "syntax-cli": "0.0.97"
+  }
+}