diff --git a/acorn-loose/src/statement.js b/acorn-loose/src/statement.js
index ac208424e..a5b574044 100644
--- a/acorn-loose/src/statement.js
+++ b/acorn-loose/src/statement.js
@@ -10,9 +10,7 @@ lp.parseTopLevel = function() {
   while (this.tok.type !== tt.eof) node.body.push(this.parseStatement())
   this.toks.adaptDirectivePrologue(node.body)
   this.last = this.tok
-  if (this.options.ecmaVersion >= 6) {
-    node.sourceType = this.options.sourceType
-  }
+  node.sourceType = this.options.sourceType
   return this.finishNode(node, "Program")
 }
 
diff --git a/acorn/CHANGELOG.md b/acorn/CHANGELOG.md
index f2cd6a4b6..1438da677 100644
--- a/acorn/CHANGELOG.md
+++ b/acorn/CHANGELOG.md
@@ -1,3 +1,15 @@
+## 6.4.0 (2019-11-26)
+
+### New features
+
+Add a static `acorn` property to the `Parser` class that contains the entire module interface, to allow plugins to access the instance of the library that they are acting on.
+
+## 6.3.0 (2019-08-12)
+
+### New features
+
+`sourceType: "module"` can now be used even when `ecmaVersion` is less than 6, to parse module-style code that otherwise conforms to an older standard.
+
 ## 6.2.1 (2019-07-21)
 
 ### Bug fixes
diff --git a/acorn/README.md b/acorn/README.md
index fa372ee68..bcf85ccba 100644
--- a/acorn/README.md
+++ b/acorn/README.md
@@ -64,6 +64,9 @@ an object containing any of these fields:
   either `"script"` or `"module"`. This influences global strict mode
   and parsing of `import` and `export` declarations.
 
+  **NOTE**: If set to `"module"`, then static `import` / `export` syntax
+  will be valid, even if `ecmaVersion` is less than 6.
+
 - **onInsertedSemicolon**: If given a callback, that callback will be
   called whenever a missing semicolon is inserted by the parser. The
   callback will be given the character offset of the point where the
diff --git a/acorn/dist/acorn.d.ts b/acorn/dist/acorn.d.ts
index 9d6bb784f..c68e23912 100644
--- a/acorn/dist/acorn.d.ts
+++ b/acorn/dist/acorn.d.ts
@@ -36,14 +36,14 @@ declare namespace acorn {
 
   class Parser {
     constructor(options: Options, input: string, startPos?: number)
-    parse(): Node
-    static parse(input: string, options?: Options): Node
-    static parseExpressionAt(input: string, pos: number, options?: Options): Node
-    static tokenizer(input: string, options?: Options): {
+    parse(this: Parser): Node
+    static parse(this: typeof Parser, input: string, options?: Options): Node
+    static parseExpressionAt(this: typeof Parser, input: string, pos: number, options?: Options): Node
+    static tokenizer(this: typeof Parser, input: string, options?: Options): {
       getToken(): Token
       [Symbol.iterator](): Iterator<Token>
     }
-    static extend(...plugins: ((BaseParser: typeof Parser) => typeof Parser)[]): typeof Parser
+    static extend(this: typeof Parser, ...plugins: ((BaseParser: typeof Parser) => typeof Parser)[]): typeof Parser
   }
 
   interface Position { line: number; column: number; offset: number }
diff --git a/acorn/package.json b/acorn/package.json
index c6f812313..318bed138 100644
--- a/acorn/package.json
+++ b/acorn/package.json
@@ -4,7 +4,7 @@
   "homepage": "https://github.com/acornjs/acorn",
   "main": "dist/acorn.js",
   "module": "dist/acorn.mjs",
-  "version": "6.2.1",
+  "version": "6.4.1",
   "engines": {"node": ">=0.4.0"},
   "maintainers": [
     {
diff --git a/acorn/src/expression.js b/acorn/src/expression.js
index 7a4aed93b..b338141e8 100644
--- a/acorn/src/expression.js
+++ b/acorn/src/expression.js
@@ -272,7 +272,7 @@ pp.parseSubscript = function(base, startPos, startLoc, noCalls, maybeAsyncArrow)
   if (computed || this.eat(tt.dot)) {
     let node = this.startNodeAt(startPos, startLoc)
     node.object = base
-    node.property = computed ? this.parseExpression() : this.parseIdent(true)
+    node.property = computed ? this.parseExpression() : this.parseIdent(this.options.allowReserved !== "never")
     node.computed = !!computed
     if (computed) this.expect(tt.bracketR)
     base = this.finishNode(node, "MemberExpression")
@@ -734,7 +734,7 @@ pp.parsePropertyName = function(prop) {
       prop.computed = false
     }
   }
-  return prop.key = this.type === tt.num || this.type === tt.string ? this.parseExprAtom() : this.parseIdent(true)
+  return prop.key = this.type === tt.num || this.type === tt.string ? this.parseExprAtom() : this.parseIdent(this.options.allowReserved !== "never")
 }
 
 // Initialize empty function node.
@@ -902,7 +902,6 @@ pp.checkUnreserved = function({start, end, name}) {
 
 pp.parseIdent = function(liberal, isBinding) {
   let node = this.startNode()
-  if (liberal && this.options.allowReserved === "never") liberal = false
   if (this.type === tt.name) {
     node.name = this.value
   } else if (this.type.keyword) {
diff --git a/acorn/src/identifier.js b/acorn/src/identifier.js
index c768a2d79..339066260 100644
--- a/acorn/src/identifier.js
+++ b/acorn/src/identifier.js
@@ -14,6 +14,7 @@ const ecma5AndLessKeywords = "break case catch continue debugger default do else
 
 export const keywords = {
   5: ecma5AndLessKeywords,
+  "5module": ecma5AndLessKeywords + " export import",
   6: ecma5AndLessKeywords + " const class extends export import super"
 }
 
diff --git a/acorn/src/index.js b/acorn/src/index.js
index 1fb6877ff..506a989dd 100644
--- a/acorn/src/index.js
+++ b/acorn/src/index.js
@@ -22,17 +22,58 @@ import "./expression"
 import "./location"
 import "./scope"
 
-export {Parser} from "./state"
-export {defaultOptions} from "./options"
-export {Position, SourceLocation, getLineInfo} from "./locutil"
-export {Node} from "./node"
-export {TokenType, types as tokTypes, keywords as keywordTypes} from "./tokentype"
-export {TokContext, types as tokContexts} from "./tokencontext"
-export {isIdentifierChar, isIdentifierStart} from "./identifier"
-export {Token} from "./tokenize"
-export {isNewLine, lineBreak, lineBreakG, nonASCIIwhitespace} from "./whitespace"
-
-export const version = "6.2.1"
+import {defaultOptions} from "./options"
+import {Position, SourceLocation, getLineInfo} from "./locutil"
+import {Node} from "./node"
+import {TokenType, types as tokTypes, keywords as keywordTypes} from "./tokentype"
+import {TokContext, types as tokContexts} from "./tokencontext"
+import {isIdentifierChar, isIdentifierStart} from "./identifier"
+import {Token} from "./tokenize"
+import {isNewLine, lineBreak, lineBreakG, nonASCIIwhitespace} from "./whitespace"
+
+export const version = "6.4.0"
+export {
+  Parser,
+  defaultOptions,
+  Position,
+  SourceLocation,
+  getLineInfo,
+  Node,
+  TokenType,
+  tokTypes,
+  keywordTypes,
+  TokContext,
+  tokContexts,
+  isIdentifierChar,
+  isIdentifierStart,
+  Token,
+  isNewLine,
+  lineBreak,
+  lineBreakG,
+  nonASCIIwhitespace
+}
+
+Parser.acorn = {
+  Parser,
+  version,
+  defaultOptions,
+  Position,
+  SourceLocation,
+  getLineInfo,
+  Node,
+  TokenType,
+  tokTypes,
+  keywordTypes,
+  TokContext,
+  tokContexts,
+  isIdentifierChar,
+  isIdentifierStart,
+  Token,
+  isNewLine,
+  lineBreak,
+  lineBreakG,
+  nonASCIIwhitespace
+}
 
 // The main exported interface (under `self.acorn` when in the
 // browser) is a `parse` function that takes a code string and
diff --git a/acorn/src/regexp.js b/acorn/src/regexp.js
index ee19bcf55..2fe832b4b 100644
--- a/acorn/src/regexp.js
+++ b/acorn/src/regexp.js
@@ -50,7 +50,8 @@ export class RegExpValidationState {
     if (!this.switchU || c <= 0xD7FF || c >= 0xE000 || i + 1 >= l) {
       return c
     }
-    return (c << 10) + s.charCodeAt(i + 1) - 0x35FDC00
+    const next = s.charCodeAt(i + 1)
+    return next >= 0xDC00 && next <= 0xDFFF ? (c << 10) + next - 0x35FDC00 : c
   }
 
   nextIndex(i) {
@@ -59,8 +60,9 @@ export class RegExpValidationState {
     if (i >= l) {
       return l
     }
-    const c = s.charCodeAt(i)
-    if (!this.switchU || c <= 0xD7FF || c >= 0xE000 || i + 1 >= l) {
+    let c = s.charCodeAt(i), next
+    if (!this.switchU || c <= 0xD7FF || c >= 0xE000 || i + 1 >= l ||
+        (next = s.charCodeAt(i + 1)) < 0xDC00 || next > 0xDFFF) {
       return i + 1
     }
     return i + 2
diff --git a/acorn/src/state.js b/acorn/src/state.js
index 73e49b9f3..eb4e0e120 100644
--- a/acorn/src/state.js
+++ b/acorn/src/state.js
@@ -9,7 +9,7 @@ export class Parser {
   constructor(options, input, startPos) {
     this.options = options = getOptions(options)
     this.sourceFile = options.sourceFile
-    this.keywords = wordsRegexp(keywords[options.ecmaVersion >= 6 ? 6 : 5])
+    this.keywords = wordsRegexp(keywords[options.ecmaVersion >= 6 ? 6 : options.sourceType === "module" ? "5module" : 5])
     let reserved = ""
     if (options.allowReserved !== true) {
       for (let v = options.ecmaVersion;; v--)
diff --git a/acorn/src/statement.js b/acorn/src/statement.js
index d423b5910..8cadb5118 100644
--- a/acorn/src/statement.js
+++ b/acorn/src/statement.js
@@ -27,9 +27,7 @@ pp.parseTopLevel = function(node) {
       this.raiseRecoverable(this.undefinedExports[name].start, `Export '${name}' is not defined`)
   this.adaptDirectivePrologue(node.body)
   this.next()
-  if (this.options.ecmaVersion >= 6) {
-    node.sourceType = this.options.sourceType
-  }
+  node.sourceType = this.options.sourceType
   return this.finishNode(node, "Program")
 }
 
diff --git a/test/tests-regexp.js b/test/tests-regexp.js
index 6c4719486..804e00a59 100644
--- a/test/tests-regexp.js
+++ b/test/tests-regexp.js
@@ -1049,6 +1049,7 @@ test("/[\\d][\\12-\\14]{1,}[^\\d]/", {}, { ecmaVersion: 2015 })
 testFail("/[\\d][\\12-\\14]{1,}[^\\d]/u", "Invalid regular expression flag (1:1)", { ecmaVersion: 5 })
 testFail("/[\\d][\\12-\\14]{1,}[^\\d]/u", "Invalid regular expression: /[\\d][\\12-\\14]{1,}[^\\d]/: Invalid class escape (1:1)", { ecmaVersion: 2015 })
 test("/([a ]\\b)*\\b/", {}, { ecmaVersion: 5 })
+test("/[x-*]/u".replace("*", String.fromCharCode(0xd800)), {}, {ecmaVersion: 6})
 
 /*
 // This is test case generator.
diff --git a/test/tests.js b/test/tests.js
index ca07b3a71..35fe29ca5 100644
--- a/test/tests.js
+++ b/test/tests.js
@@ -7,6 +7,62 @@ if (typeof exports != "undefined") {
   var acorn = require("../acorn");
 }
 
+test("import ''", {
+  type: "Program",
+  start: 0,
+  end: 9,
+  body: [
+    {
+      type: "ImportDeclaration",
+      start: 0,
+      end: 9,
+      specifiers: [],
+      source: {
+        type: "Literal",
+        start: 7,
+        end: 9,
+        value: "",
+        raw: "''"
+      }
+    }
+  ]
+}, {
+  ecmaVersion: 5,
+  sourceType: "module"
+});
+
+testFail("import('')", "Unexpected token (1:6)", {
+  ecmaVersion: 5,
+  sourceType: "module"
+});
+
+test("new Object", {
+  type: "Program",
+  start: 0,
+  end: 10,
+  body: [
+    {
+      type: "ExpressionStatement",
+      start: 0,
+      end: 10,
+      expression: {
+        type: "NewExpression",
+        start: 0,
+        end: 10,
+        callee: {
+          type: "Identifier",
+          start: 4,
+          end: 10,
+          name: "Object"
+        },
+        arguments: []
+      }
+    }
+  ]
+}, {
+  allowReserved: "never"
+});
+
 test("this\n", {
   type: "Program",
   body: [