diff --git a/Sources/_MatchingEngine/Regex/Parse/Mocking.swift b/Sources/_MatchingEngine/Regex/Parse/Mocking.swift
index b2bd6902..e3a178a1 100644
--- a/Sources/_MatchingEngine/Regex/Parse/Mocking.swift
+++ b/Sources/_MatchingEngine/Regex/Parse/Mocking.swift
@@ -15,11 +15,13 @@
 enum Delimiter: Hashable, CaseIterable {
   case traditional
   case experimental
+  case reSingleQuote
 
   var openingAndClosing: (opening: String, closing: String) {
     switch self {
-    case .traditional: return ("'/", "/'")
-    case .experimental: return ("'|", "|'")
+    case .traditional: return ("#/", "/#")
+    case .experimental: return ("#|", "|#")
+    case .reSingleQuote: return ("re'", "'")
     }
   }
   var opening: String { openingAndClosing.opening }
@@ -28,8 +30,10 @@ enum Delimiter: Hashable, CaseIterable {
   /// The default set of syntax options that the delimiter indicates.
   var defaultSyntaxOptions: SyntaxOptions {
     switch self {
-    case .traditional: return .traditional
-    case .experimental: return .experimental
+    case .traditional, .reSingleQuote:
+      return .traditional
+    case .experimental:
+      return .experimental
     }
   }
 }
diff --git a/Tests/RegexTests/LexTests.swift b/Tests/RegexTests/LexTests.swift
index ce82f8b8..25ced92c 100644
--- a/Tests/RegexTests/LexTests.swift
+++ b/Tests/RegexTests/LexTests.swift
@@ -102,23 +102,26 @@ extension RegexTests {
 
   func testCompilerInterface() {
     let testCases: [(String, (String, Delimiter)?)] = [
-      ("'/abc/'", ("abc", .traditional)),
-      ("'|abc|'", ("abc", .experimental)),
+      ("#/abc/#", ("abc", .traditional)),
+      ("#|abc|#", ("abc", .experimental)),
 
       // TODO: Null characters are lexically valid, similar to string literals,
       // but we ought to warn the user about them.
-      ("'|ab\0c|'", ("ab\0c", .experimental)),
+      ("#|ab\0c|#", ("ab\0c", .experimental)),
       ("'abc'", nil),
-      ("'/abc/def/'", ("abc/def", .traditional)),
-      ("'|abc|def|'", ("abc|def", .experimental)),
-      ("'/abc\\/'def/'", ("abc\\/'def", .traditional)),
-      ("'|abc\\|'def|'", ("abc\\|'def", .experimental)),
-      ("'/abc|'def/'", ("abc|'def", .traditional)),
-      ("'|abc/'def|'", ("abc/'def", .experimental)),
-      ("'/abc|'def/", nil),
-      ("'|abc/'def'", nil),
-      ("'/abc\n/'", nil),
-      ("'/abc\r/'", nil),
+      ("#/abc/def/#", ("abc/def", .traditional)),
+      ("#|abc|def|#", ("abc|def", .experimental)),
+      ("#/abc\\/#def/#", ("abc\\/#def", .traditional)),
+      ("#|abc\\|#def|#", ("abc\\|#def", .experimental)),
+      ("#/abc|#def/#", ("abc|#def", .traditional)),
+      ("#|abc/#def|#", ("abc/#def", .experimental)),
+      ("#/abc|#def/", nil),
+      ("#|abc/#def#", nil),
+      ("#/abc\n/#", nil),
+      ("#/abc\r/#", nil),
+
+      (#"re'abcre\''"#, (#"abcre\'"#, .reSingleQuote)),
+      (#"re'\'"#, nil)
     ]
 
     for (input, expected) in testCases {
diff --git a/Tests/RegexTests/ParseTests.swift b/Tests/RegexTests/ParseTests.swift
index ac062111..4872e256 100644
--- a/Tests/RegexTests/ParseTests.swift
+++ b/Tests/RegexTests/ParseTests.swift
@@ -1436,31 +1436,33 @@ extension RegexTests {
 
     // MARK: Parse with delimiters
 
-    parseWithDelimitersTest("'/a b/'", concat("a", " ", "b"))
-    parseWithDelimitersTest("'|a b|'", concat("a", "b"))
+    parseWithDelimitersTest("#/a b/#", concat("a", " ", "b"))
+    parseWithDelimitersTest("#|a b|#", concat("a", "b"))
 
-    parseWithDelimitersTest("'|[a b]|'", charClass("a", "b"))
+    parseWithDelimitersTest("#|[a b]|#", charClass("a", "b"))
     parseWithDelimitersTest(
-      "'|(?-x)[a b]|'", changeMatchingOptions(
+      "#|(?-x)[a b]|#", changeMatchingOptions(
         matchingOptions(removing: .extended), isIsolated: true,
         charClass("a", " ", "b"))
     )
-    parseWithDelimitersTest("'|[[a ] b]|'", charClass(charClass("a"), "b"))
+    parseWithDelimitersTest("#|[[a ] b]|#", charClass(charClass("a"), "b"))
 
     // Non-semantic whitespace between quantifier characters for consistency
     // with PCRE.
-    parseWithDelimitersTest("'|a * ?|'", zeroOrMore(.reluctant, of: "a"))
+    parseWithDelimitersTest("#|a * ?|#", zeroOrMore(.reluctant, of: "a"))
 
     // End-of-line comments aren't enabled by default in experimental syntax.
-    parseWithDelimitersTest("'|#abc|'", concat("#", "a", "b", "c"))
-    parseWithDelimitersTest("'|(?x)#abc|'", changeMatchingOptions(
+    parseWithDelimitersTest("#|#abc|#", concat("#", "a", "b", "c"))
+    parseWithDelimitersTest("#|(?x)#abc|#", changeMatchingOptions(
       matchingOptions(adding: .extended), isIsolated: true,
       empty())
     )
 
-    parseWithDelimitersTest("'|||'", alt(empty(), empty()))
-    parseWithDelimitersTest("'||||'", alt(empty(), empty(), empty()))
-    parseWithDelimitersTest("'|a||'", alt("a", empty()))
+    parseWithDelimitersTest("#|||#", alt(empty(), empty()))
+    parseWithDelimitersTest("#||||#", alt(empty(), empty(), empty()))
+    parseWithDelimitersTest("#|a||#", alt("a", empty()))
+
+    parseWithDelimitersTest("re'x*'", zeroOrMore(of: "x"))
 
     // MARK: Parse not-equal
 
@@ -1878,6 +1880,6 @@ extension RegexTests {
 
   func testlibswiftDiagnostics() {
     libswiftDiagnosticMessageTest(
-      "'/[x*/'", "cannot parse regular expression: expected ']'")
+      "#/[x*/#", "cannot parse regular expression: expected ']'")
   }
 }