diff --git a/src/ast.ts b/src/ast.ts
index de52e27c..738e3778 100644
--- a/src/ast.ts
+++ b/src/ast.ts
@@ -240,11 +240,11 @@ export abstract class Node {
     return expr;
   }
 
-  static createRegexpLiteralExpression(pattern: string, modifiers: string, range: Range): RegexpLiteralExpression {
+  static createRegexpLiteralExpression(pattern: string, flags: string, range: Range): RegexpLiteralExpression {
     var expr = new RegexpLiteralExpression();
     expr.range = range;
     expr.pattern = pattern;
-    expr.modifiers = modifiers;
+    expr.patternFlags = flags;
     return expr;
   }
 
@@ -1048,14 +1048,14 @@ export class RegexpLiteralExpression extends LiteralExpression {
 
   /** Regular expression pattern. */
   pattern: string;
-  /** Regular expression modifiers. */
-  modifiers: string;
+  /** Regular expression flags. */
+  patternFlags: string;
 
   serialize(sb: string[]): void {
     sb.push("/");
     sb.push(this.pattern);
     sb.push("/");
-    sb.push(this.modifiers);
+    sb.push(this.patternFlags);
   }
 }
 
diff --git a/src/diagnosticMessages.generated.ts b/src/diagnosticMessages.generated.ts
index 42853df5..8fbbf4eb 100644
--- a/src/diagnosticMessages.generated.ts
+++ b/src/diagnosticMessages.generated.ts
@@ -10,6 +10,7 @@ export enum DiagnosticCode {
   Type_0_cannot_be_changed_to_type_1 = 106,
   Structs_cannot_extend_classes_and_vice_versa = 107,
   Structs_cannot_implement_interfaces = 108,
+  Invalid_regular_expression_flags = 109,
   Unterminated_string_literal = 1002,
   Identifier_expected = 1003,
   _0_expected = 1005,
@@ -95,6 +96,7 @@ export function diagnosticCodeToString(code: DiagnosticCode): string {
     case 106: return "Type '{0}' cannot be changed to type '{1}'.";
     case 107: return "Structs cannot extend classes and vice-versa.";
     case 108: return "Structs cannot implement interfaces.";
+    case 109: return "Invalid regular expression flags.";
     case 1002: return "Unterminated string literal.";
     case 1003: return "Identifier expected.";
     case 1005: return "'{0}' expected.";
diff --git a/src/diagnosticMessages.json b/src/diagnosticMessages.json
index 6eddbf63..192eea18 100644
--- a/src/diagnosticMessages.json
+++ b/src/diagnosticMessages.json
@@ -8,6 +8,7 @@
   "Type '{0}' cannot be changed to type '{1}'.": 106,
   "Structs cannot extend classes and vice-versa.": 107,
   "Structs cannot implement interfaces.": 108,
+  "Invalid regular expression flags.": 109,
 
   "Unterminated string literal.": 1002,
   "Identifier expected.": 1003,
diff --git a/src/parser.ts b/src/parser.ts
index 649e6395..e6168143 100644
--- a/src/parser.ts
+++ b/src/parser.ts
@@ -1426,8 +1426,11 @@ export class Parser extends DiagnosticEmitter {
           return Node.createNewExpression((<CallExpression>operand).expression, (<CallExpression>operand).typeArguments, (<CallExpression>operand).arguments, tn.range(startPos, tn.pos));
         this.error(DiagnosticCode.Operation_not_supported, tn.range());
         return null;
-      } else
+      } else {
         operand = this.parseExpression(tn, p);
+        if (!operand)
+          return null;
+      }
 
       // UnaryPrefixExpression
       if (token == Token.PLUS_PLUS || token == Token.MINUS_MINUS)
@@ -1513,15 +1516,14 @@ export class Parser extends DiagnosticEmitter {
         return Node.createFloatLiteralExpression(tn.readFloat(), tn.range(startPos, tn.pos));
 
       // RegexpLiteralExpression
+      // note that this also continues on invalid ones so the surrounding AST remains intact
       case Token.SLASH:
-        var regexpPattern = tn.readRegexpPattern();
-        if (regexpPattern == null)
-          return null;
+        var regexpPattern = tn.readRegexpPattern(); // also reports
         if (!tn.skip(Token.SLASH)) {
           this.error(DiagnosticCode._0_expected, tn.range(), "/");
           return null;
         }
-        return Node.createRegexpLiteralExpression(regexpPattern, tn.readRegexpModifiers(), tn.range(startPos, tn.pos));
+        return Node.createRegexpLiteralExpression(regexpPattern, tn.readRegexpFlags() /* also reports */, tn.range(startPos, tn.pos));
 
       default:
         this.error(DiagnosticCode.Expression_expected, tn.range());
diff --git a/src/tokenizer.ts b/src/tokenizer.ts
index c99b314b..f36bca78 100644
--- a/src/tokenizer.ts
+++ b/src/tokenizer.ts
@@ -901,14 +901,14 @@ export class Tokenizer extends DiagnosticEmitter {
     }
   }
 
-  readRegexpPattern(): string | null {
+  readRegexpPattern(): string {
     var text = this.source.text;
     var start = this.pos;
     var escaped = false;
     while (true) {
       if (this.pos >= this.end) {
         this.error(DiagnosticCode.Unterminated_regular_expression_literal, this.range(start, this.end));
-        return null;
+        break;
       }
       if (text.charCodeAt(this.pos) == CharCode.BACKSLASH) {
         ++this.pos;
@@ -920,7 +920,7 @@ export class Tokenizer extends DiagnosticEmitter {
         break;
       if (isLineBreak(c)) {
         this.error(DiagnosticCode.Unterminated_regular_expression_literal, this.range(start, this.pos));
-        return null;
+        break;
       }
       ++this.pos;
       escaped = false;
@@ -928,23 +928,35 @@ export class Tokenizer extends DiagnosticEmitter {
     return text.substring(start, this.pos);
   }
 
-  readRegexpModifiers(): string {
+  readRegexpFlags(): string {
     var text = this.source.text;
     var start = this.pos;
-    /a/
+    var flags = 0;
     while (this.pos < this.end) {
-      switch (text.charCodeAt(this.pos)) {
+      var c: i32 = text.charCodeAt(this.pos);
+      if (!isIdentifierPart(c))
+        break;
+      ++this.pos;
+      switch (c) {
 
+        // make sure each supported flag is unique
         case CharCode.g:
+          flags |= select<i32>(1, -1, !(flags & 1));
+          break;
         case CharCode.i:
+          flags |= select<i32>(2, -1, !(flags & 2));
+          break;
         case CharCode.m:
-          ++this.pos;
+          flags |= select<i32>(4, -1, !(flags & 4));
           break;
 
         default:
-          return text.substring(start, this.pos);
+          flags = -1;
+          break;
       }
     }
+    if (flags == -1)
+      this.error(DiagnosticCode.Invalid_regular_expression_flags, this.range(start, this.pos));
     return text.substring(start, this.pos);
   }
 
diff --git a/tests/parser/regexp.ts b/tests/parser/regexp.ts
index b6451957..1d933511 100644
--- a/tests/parser/regexp.ts
+++ b/tests/parser/regexp.ts
@@ -16,3 +16,15 @@ b/ig;
 
 // just a comment
 //ig;
+
+// duplicate flags
+
+/(abc)\//iig;
+
+// invalid flags
+
+/(abc)\//iX;
+
+// surrounding AST remains intact
+
+false && /abc/gX.test(someString) || true;
diff --git a/tests/parser/regexp.ts.fixture.ts b/tests/parser/regexp.ts.fixture.ts
index a49d47de..b60acade 100644
--- a/tests/parser/regexp.ts.fixture.ts
+++ b/tests/parser/regexp.ts.fixture.ts
@@ -3,4 +3,11 @@
 let re = /(abc)\//ig;
 let noRe = !/(abc)\//i;
 b / ig;
+/(abc)\//iig;
+/(abc)\//iX;
+false && /abc/gX.test(someString) || true;
 // ERROR 1161: "Unterminated regular expression literal." in regexp.ts @ 75,76
+// ERROR 1005: "'/' expected." in regexp.ts @ 74,76
+// ERROR 109: "Invalid regular expression flags." in regexp.ts @ 95,98
+// ERROR 109: "Invalid regular expression flags." in regexp.ts @ 111,113
+// ERROR 109: "Invalid regular expression flags." in regexp.ts @ 131,133