diff --git a/Sources/_StringProcessing/MatchingOptions.swift b/Sources/_StringProcessing/MatchingOptions.swift
index d511c9f7c..60cc7d0de 100644
--- a/Sources/_StringProcessing/MatchingOptions.swift
+++ b/Sources/_StringProcessing/MatchingOptions.swift
@@ -14,7 +14,9 @@
 /// A type that represents the current state of regex matching options, with
 /// stack-based scoping.
 struct MatchingOptions {
-  fileprivate var stack: [Representation]
+  // FIXME: Workaround for rdar://104923020
+  // fileprivate
+  var stack: [Representation]
   
   fileprivate func _invariantCheck() {
     assert(!stack.isEmpty, "Unbalanced call to endScope")
@@ -125,7 +127,9 @@ extension MatchingOptions {
 // MARK: - Implementation
 extension MatchingOptions {
   /// An option that changes the behavior of a regular expression.
-  fileprivate enum Option: Int {
+  // FIXME: Workaround for rdar://104923020
+  // fileprivate
+  enum Option: Int {
     // PCRE options
     case caseInsensitive
     case allowDuplicateGroupNames
@@ -212,7 +216,9 @@ extension MatchingOptions {
 
 extension MatchingOptions {
   /// A set of matching options.
-  fileprivate struct Representation: OptionSet, RawRepresentable {
+  // FIXME: Workaround for rdar://104923020
+  // fileprivate
+  struct Representation: OptionSet, RawRepresentable {
     var rawValue: UInt32
 
     /// Returns `true` if the option denoted by `kind` is a member of this set.
diff --git a/Tests/RegexBuilderTests/CustomTests.swift b/Tests/RegexBuilderTests/CustomTests.swift
index bc71f2363..d34b5689f 100644
--- a/Tests/RegexBuilderTests/CustomTests.swift
+++ b/Tests/RegexBuilderTests/CustomTests.swift
@@ -183,7 +183,7 @@ class CustomRegexComponentTests: XCTestCase {
   // tests.
   func testCustomRegexComponents() throws {
     customTest(
-      Regex {
+      Regex<Substring> {
         Numbler()
         Asciibbler()
       },
@@ -194,7 +194,7 @@ class CustomRegexComponentTests: XCTestCase {
       ("t4", .match, nil))
 
     customTest(
-      Regex {
+      Regex<Substring> {
         OneOrMore { Numbler() }
       },
       ("ab123c", .firstMatch, "123"),
@@ -425,7 +425,7 @@ class CustomRegexComponentTests: XCTestCase {
     )
 
     customTest(
-      Regex {
+      Regex<CurrencyParser.Currency> {
         CurrencyParser()
       },
       ("USD", .usd, nil),
@@ -437,7 +437,7 @@ class CustomRegexComponentTests: XCTestCase {
 
     // No capture, two errors
     customTest(
-      Regex {
+      Regex<Substring> {
         IntParser()
         " "
         IntParser()
@@ -449,7 +449,7 @@ class CustomRegexComponentTests: XCTestCase {
     )
 
     customTest(
-      Regex {
+      Regex<Substring> {
         CurrencyParser()
         IntParser()
       },
@@ -462,7 +462,7 @@ class CustomRegexComponentTests: XCTestCase {
     // One capture, two errors: One error is thrown from inside a capture,
     // while the other one is thrown from outside
     customTest(
-      Regex {
+      Regex<(Substring, CurrencyParser.Currency)> {
         Capture { CurrencyParser() }
         IntParser()
       },
@@ -473,7 +473,7 @@ class CustomRegexComponentTests: XCTestCase {
     )
 
     customTest(
-      Regex {
+      Regex<(Substring, Int)> {
         CurrencyParser()
         Capture { IntParser() }
       },
@@ -485,7 +485,7 @@ class CustomRegexComponentTests: XCTestCase {
 
     // One capture, two errors: Both errors are thrown from inside the capture
     customTest(
-      Regex {
+      Regex<(Substring, Substring)> {
         Capture {
           CurrencyParser()
           IntParser()
@@ -499,7 +499,7 @@ class CustomRegexComponentTests: XCTestCase {
 
     // Two captures, two errors: Different erros are thrown from inside captures
     customTest(
-      Regex {
+      Regex<(Substring, CurrencyParser.Currency, Int)> {
         Capture(CurrencyParser())
         Capture(IntParser())
       },
diff --git a/Tests/RegexBuilderTests/MotivationTests.swift b/Tests/RegexBuilderTests/MotivationTests.swift
index 7dd4c77e4..f72486610 100644
--- a/Tests/RegexBuilderTests/MotivationTests.swift
+++ b/Tests/RegexBuilderTests/MotivationTests.swift
@@ -309,8 +309,8 @@ extension RegexDSLTests {
           "CREDIT"
           "DEBIT"
         }
-      } transform: {
-        TransactionKind(rawValue: String($0))
+      } transform: { (s: Substring) in
+        TransactionKind(rawValue: String(s))
       }
       
       OneOrMore(.whitespace)
@@ -322,8 +322,8 @@ extension RegexDSLTests {
         Repeat(.digit, count: 2)
         Repeat(.digit, count: 2)
         Repeat(.digit, count: 4)
-      } transform: {
-        Date(mmddyyyy: String($0))
+      } transform: { (s: Substring) in
+        Date(mmddyyyy: String(s))
       }
       
       OneOrMore(.whitespace)
@@ -345,8 +345,8 @@ extension RegexDSLTests {
         OneOrMore(.digit)
         "."
         Repeat(.digit, count: 2)
-      } transform: {
-        Double($0)
+      } transform: { (s: Substring) in
+        Double(s)
       }
     }
     
diff --git a/Tests/RegexBuilderTests/RegexDSLTests.swift b/Tests/RegexBuilderTests/RegexDSLTests.swift
index e25f2df05..8b7611536 100644
--- a/Tests/RegexBuilderTests/RegexDSLTests.swift
+++ b/Tests/RegexBuilderTests/RegexDSLTests.swift
@@ -1253,8 +1253,8 @@ class RegexDSLTests: XCTestCase {
         TryCapture(as: b) {
           "#"
           OneOrMore(.digit)
-        } transform: {
-          Int($0.dropFirst())
+        } transform: { (s: Substring) in
+          Int(s.dropFirst())
         }
       }
       a
@@ -1271,14 +1271,14 @@ class RegexDSLTests: XCTestCase {
     do {
       let a = Reference(Substring.self)
       let b = Reference(Int.self)
-      let regex = Regex {
+      let regex = Regex<(Substring, Substring, Int?, Int?, Substring?)> {
         Capture("abc", as: a)
         ZeroOrMore {
           TryCapture(as: b) {
             "#"
             OneOrMore(.digit)
-          } transform: {
-            Int($0.dropFirst())
+          } transform: { (s: Substring) -> Int? in
+            Int(s.dropFirst())
           }
         }
         a