diff --git a/Package.swift b/Package.swift
index e95d98b67..01c6adcb1 100644
--- a/Package.swift
+++ b/Package.swift
@@ -3,6 +3,13 @@
 
 import PackageDescription
 
+let availabilityDefinition = PackageDescription.SwiftSetting.unsafeFlags([
+    "-Xfrontend",
+    "-define-availability",
+    "-Xfrontend",
+    #""SwiftStdlib 5.7:macOS 9999, iOS 9999, watchOS 9999, tvOS 9999""#
+])
+
 let package = Package(
     name: "swift-experimental-string-processing",
     products: [
@@ -30,12 +37,14 @@ let package = Package(
             name: "_RegexParser",
             dependencies: [],
             swiftSettings: [
-                .unsafeFlags(["-enable-library-evolution"])
+                .unsafeFlags(["-enable-library-evolution"]),
+                availabilityDefinition
             ]),
         .testTarget(
             name: "MatchingEngineTests",
             dependencies: [
-              "_RegexParser", "_StringProcessing"]),
+                "_RegexParser", "_StringProcessing"
+            ]),
         .target(
             name: "_CUnicode",
             dependencies: []),
@@ -44,26 +53,31 @@ let package = Package(
             dependencies: ["_RegexParser", "_CUnicode"],
             swiftSettings: [
                 .unsafeFlags(["-enable-library-evolution"]),
+                availabilityDefinition
             ]),
         .target(
             name: "RegexBuilder",
             dependencies: ["_StringProcessing", "_RegexParser"],
             swiftSettings: [
                 .unsafeFlags(["-enable-library-evolution"]),
-                .unsafeFlags(["-Xfrontend", "-enable-experimental-pairwise-build-block"])
+                .unsafeFlags(["-Xfrontend", "-enable-experimental-pairwise-build-block"]),
+                availabilityDefinition
             ]),
         .testTarget(
             name: "RegexTests",
-            dependencies: ["_StringProcessing"]),
+            dependencies: ["_StringProcessing"],
+            swiftSettings: [availabilityDefinition]),
         .testTarget(
             name: "RegexBuilderTests",
             dependencies: ["_StringProcessing", "RegexBuilder"],
             swiftSettings: [
-                .unsafeFlags(["-Xfrontend", "-enable-experimental-pairwise-build-block"])
+                .unsafeFlags(["-Xfrontend", "-enable-experimental-pairwise-build-block"]),
+                availabilityDefinition
             ]),
         .target(
             name: "Prototypes",
-            dependencies: ["_RegexParser", "_StringProcessing"]),
+            dependencies: ["_RegexParser", "_StringProcessing"],
+            swiftSettings: [availabilityDefinition]),
 
         // MARK: Scripts
         .executableTarget(
@@ -84,11 +98,12 @@ let package = Package(
           name: "Exercises",
           dependencies: ["_RegexParser", "Prototypes", "_StringProcessing", "RegexBuilder"],
           swiftSettings: [
-              .unsafeFlags(["-Xfrontend", "-enable-experimental-pairwise-build-block"])
+              .unsafeFlags(["-Xfrontend", "-enable-experimental-pairwise-build-block"]),
+              availabilityDefinition
           ]),
         .testTarget(
           name: "ExercisesTests",
-          dependencies: ["Exercises"]),
+          dependencies: ["Exercises"],
+          swiftSettings: [availabilityDefinition]),
     ]
 )
-
diff --git a/Sources/RegexBuilder/Anchor.swift b/Sources/RegexBuilder/Anchor.swift
index ba910bd30..7933b987a 100644
--- a/Sources/RegexBuilder/Anchor.swift
+++ b/Sources/RegexBuilder/Anchor.swift
@@ -12,6 +12,7 @@
 import _RegexParser
 @_spi(RegexBuilder) import _StringProcessing
 
+@available(SwiftStdlib 5.7, *)
 public struct Anchor {
   internal enum Kind {
     case startOfSubject
@@ -107,6 +108,7 @@ extension Anchor {
   }
 }
 
+@available(SwiftStdlib 5.7, *)
 public struct Lookahead<Output>: _BuiltinRegexComponent {
   public var regex: Regex<Output>
 
diff --git a/Sources/RegexBuilder/Builder.swift b/Sources/RegexBuilder/Builder.swift
index 8921c8f25..be9a48e36 100644
--- a/Sources/RegexBuilder/Builder.swift
+++ b/Sources/RegexBuilder/Builder.swift
@@ -11,6 +11,7 @@
 
 @_spi(RegexBuilder) import _StringProcessing
 
+@available(SwiftStdlib 5.7, *)
 @resultBuilder
 public enum RegexComponentBuilder {
   public static func buildBlock() -> Regex<Substring> {
diff --git a/Sources/RegexBuilder/CharacterClass.swift b/Sources/RegexBuilder/CharacterClass.swift
index 78ebd49a2..99e981d33 100644
--- a/Sources/RegexBuilder/CharacterClass.swift
+++ b/Sources/RegexBuilder/CharacterClass.swift
@@ -12,6 +12,7 @@
 import _RegexParser
 @_spi(RegexBuilder) import _StringProcessing
 
+@available(SwiftStdlib 5.7, *)
 public struct CharacterClass {
   internal var ccc: DSLTree.CustomCharacterClass
   
@@ -122,6 +123,7 @@ extension CharacterClass {
 }
 
 /// Range syntax for characters in `CharacterClass`es.
+@available(SwiftStdlib 5.7, *)
 public func ...(lhs: Character, rhs: Character) -> CharacterClass {
   let range: DSLTree.CustomCharacterClass.Member = .range(.char(lhs), .char(rhs))
   let ccc = DSLTree.CustomCharacterClass(members: [range], isInverted: false)
@@ -130,6 +132,7 @@ public func ...(lhs: Character, rhs: Character) -> CharacterClass {
 
 /// Range syntax for unicode scalars in `CharacterClass`es.
 @_disfavoredOverload
+@available(SwiftStdlib 5.7, *)
 public func ...(lhs: UnicodeScalar, rhs: UnicodeScalar) -> CharacterClass {
   let range: DSLTree.CustomCharacterClass.Member = .range(.scalar(lhs), .scalar(rhs))
   let ccc = DSLTree.CustomCharacterClass(members: [range], isInverted: false)
diff --git a/Sources/RegexBuilder/DSL.swift b/Sources/RegexBuilder/DSL.swift
index 80662be41..717e172b0 100644
--- a/Sources/RegexBuilder/DSL.swift
+++ b/Sources/RegexBuilder/DSL.swift
@@ -54,6 +54,7 @@ extension _BuiltinRegexComponent {
 // Note: Quantifiers are currently gyb'd.
 
 /// Specifies how much to attempt to match when using a quantifier.
+@available(SwiftStdlib 5.7, *)
 public struct QuantificationBehavior {
   internal enum Kind {
     case eagerly
@@ -121,6 +122,7 @@ extension QuantificationBehavior {
   }
 }
 
+@available(SwiftStdlib 5.7, *)
 public struct OneOrMore<Output>: _BuiltinRegexComponent {
   public var regex: Regex<Output>
 
@@ -132,6 +134,7 @@ public struct OneOrMore<Output>: _BuiltinRegexComponent {
   // Variadics.swift.
 }
 
+@available(SwiftStdlib 5.7, *)
 public struct ZeroOrMore<Output>: _BuiltinRegexComponent {
   public var regex: Regex<Output>
 
@@ -143,6 +146,7 @@ public struct ZeroOrMore<Output>: _BuiltinRegexComponent {
   // Variadics.swift.
 }
 
+@available(SwiftStdlib 5.7, *)
 public struct Optionally<Output>: _BuiltinRegexComponent {
   public var regex: Regex<Output>
 
@@ -154,6 +158,7 @@ public struct Optionally<Output>: _BuiltinRegexComponent {
   // Variadics.swift.
 }
 
+@available(SwiftStdlib 5.7, *)
 public struct Repeat<Output>: _BuiltinRegexComponent {
   public var regex: Regex<Output>
 
@@ -179,6 +184,7 @@ public struct Repeat<Output>: _BuiltinRegexComponent {
 //   ) -> R where R.Match == (W, C...)
 // }
 
+@available(SwiftStdlib 5.7, *)
 @resultBuilder
 public struct AlternationBuilder {
   @_disfavoredOverload
@@ -201,6 +207,7 @@ public struct AlternationBuilder {
   }
 }
 
+@available(SwiftStdlib 5.7, *)
 public struct ChoiceOf<Output>: _BuiltinRegexComponent {
   public var regex: Regex<Output>
 
@@ -215,6 +222,7 @@ public struct ChoiceOf<Output>: _BuiltinRegexComponent {
 
 // MARK: - Capture
 
+@available(SwiftStdlib 5.7, *)
 public struct Capture<Output>: _BuiltinRegexComponent {
   public var regex: Regex<Output>
 
@@ -225,6 +233,7 @@ public struct Capture<Output>: _BuiltinRegexComponent {
   // Note: Public initializers are currently gyb'd. See Variadics.swift.
 }
 
+@available(SwiftStdlib 5.7, *)
 public struct TryCapture<Output>: _BuiltinRegexComponent {
   public var regex: Regex<Output>
 
@@ -239,6 +248,7 @@ public struct TryCapture<Output>: _BuiltinRegexComponent {
 
 /// An atomic group, i.e. opens a local backtracking scope which, upon successful exit,
 /// discards any remaining backtracking points from within the scope
+@available(SwiftStdlib 5.7, *)
 public struct Local<Output>: _BuiltinRegexComponent {
   public var regex: Regex<Output>
 
@@ -249,6 +259,7 @@ public struct Local<Output>: _BuiltinRegexComponent {
 
 // MARK: - Backreference
 
+@available(SwiftStdlib 5.7, *)
 public struct Reference<Capture>: RegexComponent {
   let id = ReferenceID()
 
diff --git a/Sources/RegexBuilder/Match.swift b/Sources/RegexBuilder/Match.swift
index e6718d96b..32dc889d9 100644
--- a/Sources/RegexBuilder/Match.swift
+++ b/Sources/RegexBuilder/Match.swift
@@ -12,12 +12,14 @@
 import _StringProcessing
 
 extension String {
+  @available(SwiftStdlib 5.7, *)
   public func wholeMatch<R: RegexComponent>(
     @RegexComponentBuilder of content: () -> R
   ) -> Regex<R.Output>.Match? {
     wholeMatch(of: content())
   }
 
+  @available(SwiftStdlib 5.7, *)
   public func prefixMatch<R: RegexComponent>(
     @RegexComponentBuilder of content: () -> R
   ) -> Regex<R.Output>.Match? {
@@ -26,12 +28,14 @@ extension String {
 }
 
 extension Substring {
+  @available(SwiftStdlib 5.7, *)
   public func wholeMatch<R: RegexComponent>(
     @RegexComponentBuilder of content: () -> R
   ) -> Regex<R.Output>.Match? {
     wholeMatch(of: content())
   }
 
+  @available(SwiftStdlib 5.7, *)
   public func prefixMatch<R: RegexComponent>(
     @RegexComponentBuilder of content: () -> R
   ) -> Regex<R.Output>.Match? {
diff --git a/Sources/_StringProcessing/Algorithms/Algorithms/Contains.swift b/Sources/_StringProcessing/Algorithms/Algorithms/Contains.swift
index 46568192f..2f38095d8 100644
--- a/Sources/_StringProcessing/Algorithms/Algorithms/Contains.swift
+++ b/Sources/_StringProcessing/Algorithms/Algorithms/Contains.swift
@@ -27,6 +27,7 @@ extension Collection where Element: Equatable {
   /// - Parameter other: A sequence to search for within this collection.
   /// - Returns: `true` if the collection contains the specified sequence,
   /// otherwise `false`.
+  @available(SwiftStdlib 5.7, *)
   public func contains<S: Sequence>(_ other: S) -> Bool
     where S.Element == Element
   {
@@ -50,6 +51,7 @@ extension BidirectionalCollection where SubSequence == Substring {
   /// - Parameter regex: A regex to search for within this collection.
   /// - Returns: `true` if the regex was found in the collection, otherwise
   /// `false`.
+  @available(SwiftStdlib 5.7, *)
   public func contains<R: RegexComponent>(_ regex: R) -> Bool {
     contains(RegexConsumer(regex))
   }
diff --git a/Sources/_StringProcessing/Algorithms/Algorithms/FirstRange.swift b/Sources/_StringProcessing/Algorithms/Algorithms/FirstRange.swift
index 405fe47ef..e75cdbdc4 100644
--- a/Sources/_StringProcessing/Algorithms/Algorithms/FirstRange.swift
+++ b/Sources/_StringProcessing/Algorithms/Algorithms/FirstRange.swift
@@ -37,6 +37,7 @@ extension Collection where Element: Equatable {
   /// - Parameter sequence: The sequence to search for.
   /// - Returns: A range in the collection of the first occurrence of `sequence`.
   /// Returns nil if `sequence` is not found.
+  @available(SwiftStdlib 5.7, *)
   public func firstRange<S: Sequence>(
     of sequence: S
   ) -> Range<Index>? where S.Element == Element {
@@ -52,6 +53,7 @@ extension BidirectionalCollection where Element: Comparable {
   /// - Parameter other: The sequence to search for.
   /// - Returns: A range in the collection of the first occurrence of `sequence`.
   /// Returns `nil` if `sequence` is not found.
+  @available(SwiftStdlib 5.7, *)
   public func firstRange<S: Sequence>(
     of other: S
   ) -> Range<Index>? where S.Element == Element {
@@ -71,6 +73,7 @@ extension BidirectionalCollection where SubSequence == Substring {
   /// - Parameter regex: The regex to search for.
   /// - Returns: A range in the collection of the first occurrence of `regex`.
   /// Returns `nil` if `regex` is not found.
+  @available(SwiftStdlib 5.7, *)
   public func firstRange<R: RegexComponent>(of regex: R) -> Range<Index>? {
     firstRange(of: RegexConsumer(regex))
   }
diff --git a/Sources/_StringProcessing/Algorithms/Algorithms/Replace.swift b/Sources/_StringProcessing/Algorithms/Algorithms/Replace.swift
index bc23a284c..4a6da6c10 100644
--- a/Sources/_StringProcessing/Algorithms/Algorithms/Replace.swift
+++ b/Sources/_StringProcessing/Algorithms/Algorithms/Replace.swift
@@ -77,6 +77,7 @@ extension RangeReplaceableCollection where Element: Equatable {
   ///   to replace. Default is `Int.max`.
   /// - Returns: A new collection in which all occurrences of `other` in
   /// `subrange` of the collection are replaced by `replacement`.
+  @available(SwiftStdlib 5.7, *)
   public func replacing<S: Sequence, Replacement: Collection>(
     _ other: S,
     with replacement: Replacement,
@@ -99,6 +100,7 @@ extension RangeReplaceableCollection where Element: Equatable {
   ///   to replace. Default is `Int.max`.
   /// - Returns: A new collection in which all occurrences of `other` in
   /// `subrange` of the collection are replaced by `replacement`.
+  @available(SwiftStdlib 5.7, *)
   public func replacing<S: Sequence, Replacement: Collection>(
     _ other: S,
     with replacement: Replacement,
@@ -117,6 +119,7 @@ extension RangeReplaceableCollection where Element: Equatable {
   ///   - replacement: The new elements to add to the collection.
   ///   - maxReplacements: A number specifying how many occurrences of `other`
   ///   to replace. Default is `Int.max`.
+  @available(SwiftStdlib 5.7, *)
   public mutating func replace<S: Sequence, Replacement: Collection>(
     _ other: S,
     with replacement: Replacement,
@@ -184,6 +187,7 @@ extension RangeReplaceableCollection where SubSequence == Substring {
   ///   sequence matching `regex` to replace. Default is `Int.max`.
   /// - Returns: A new collection in which all occurrences of subsequence
   /// matching `regex` in `subrange` are replaced by `replacement`.
+  @available(SwiftStdlib 5.7, *)
   public func replacing<R: RegexComponent, Replacement: Collection>(
     _ regex: R,
     with replacement: Replacement,
@@ -206,6 +210,7 @@ extension RangeReplaceableCollection where SubSequence == Substring {
   ///   sequence matching `regex` to replace. Default is `Int.max`.
   /// - Returns: A new collection in which all occurrences of subsequence
   /// matching `regex` are replaced by `replacement`.
+  @available(SwiftStdlib 5.7, *)
   public func replacing<R: RegexComponent, Replacement: Collection>(
     _ regex: R,
     with replacement: Replacement,
@@ -225,6 +230,7 @@ extension RangeReplaceableCollection where SubSequence == Substring {
   ///   - replacement: The new elements to add to the collection.
   ///   - maxReplacements: A number specifying how many occurrences of the
   ///   sequence matching `regex` to replace. Default is `Int.max`.
+  @available(SwiftStdlib 5.7, *)
   public mutating func replace<R: RegexComponent, Replacement: Collection>(
     _ regex: R,
     with replacement: Replacement,
diff --git a/Sources/_StringProcessing/Algorithms/Algorithms/StartsWith.swift b/Sources/_StringProcessing/Algorithms/Algorithms/StartsWith.swift
index 346094f9e..01572fe49 100644
--- a/Sources/_StringProcessing/Algorithms/Algorithms/StartsWith.swift
+++ b/Sources/_StringProcessing/Algorithms/Algorithms/StartsWith.swift
@@ -53,6 +53,7 @@ extension BidirectionalCollection where SubSequence == Substring {
   /// - Parameter regex: A regex to compare to this sequence.
   /// - Returns: `true` if the initial elements of the sequence matches the
   /// beginning of `regex`; otherwise, `false`.
+  @available(SwiftStdlib 5.7, *)
   public func starts<R: RegexComponent>(with regex: R) -> Bool {
     starts(with: RegexConsumer(regex))
   }
diff --git a/Sources/_StringProcessing/Algorithms/Algorithms/Trim.swift b/Sources/_StringProcessing/Algorithms/Algorithms/Trim.swift
index ed7cd7bc4..fd0dbefdb 100644
--- a/Sources/_StringProcessing/Algorithms/Algorithms/Trim.swift
+++ b/Sources/_StringProcessing/Algorithms/Algorithms/Trim.swift
@@ -111,6 +111,7 @@ extension Collection {
 }
 
 extension Collection where SubSequence == Self {
+  @available(SwiftStdlib 5.7, *)
   public mutating func trimPrefix(
     while predicate: @escaping (Element) -> Bool
   ) {
@@ -121,6 +122,7 @@ extension Collection where SubSequence == Self {
 
 extension RangeReplaceableCollection {
   @_disfavoredOverload
+  @available(SwiftStdlib 5.7, *)
   public mutating func trimPrefix(
     while predicate: @escaping (Element) -> Bool
   ) {
@@ -185,6 +187,7 @@ extension Collection where Element: Equatable {
   /// element should be removed from the collection.
   /// - Returns: A collection containing the elements of the collection that are
   ///  not removed by `predicate`.
+  @available(SwiftStdlib 5.7, *)
   public func trimmingPrefix<Prefix: Collection>(
     _ prefix: Prefix
   ) -> SubSequence where Prefix.Element == Element {
@@ -198,6 +201,7 @@ extension Collection where SubSequence == Self, Element: Equatable {
   /// - Parameter predicate: A closure that takes an element of the sequence
   /// as its argument and returns a Boolean value indicating whether the
   /// element should be removed from the collection.
+  @available(SwiftStdlib 5.7, *)
   public mutating func trimPrefix<Prefix: Collection>(
     _ prefix: Prefix
   ) where Prefix.Element == Element {
@@ -212,6 +216,7 @@ extension RangeReplaceableCollection where Element: Equatable {
   /// - Parameter predicate: A closure that takes an element of the sequence
   /// as its argument and returns a Boolean value indicating whether the
   /// element should be removed from the collection.
+  @available(SwiftStdlib 5.7, *)
   public mutating func trimPrefix<Prefix: Collection>(
     _ prefix: Prefix
   ) where Prefix.Element == Element {
@@ -279,6 +284,7 @@ extension BidirectionalCollection where SubSequence == Substring {
   /// - Parameter prefix: The collection to remove from this collection.
   /// - Returns: A collection containing the elements that does not match
   /// `prefix` from the start.
+  @available(SwiftStdlib 5.7, *)
   public func trimmingPrefix<R: RegexComponent>(_ regex: R) -> SubSequence {
     trimmingPrefix(RegexConsumer(regex))
   }
@@ -297,6 +303,7 @@ extension RangeReplaceableCollection
 {
   /// Removes the initial elements that matches the given regex.
   /// - Parameter regex: The regex to remove from this collection.
+  @available(SwiftStdlib 5.7, *)
   public mutating func trimPrefix<R: RegexComponent>(_ regex: R) {
     trimPrefix(RegexConsumer(regex))
   }
diff --git a/Sources/_StringProcessing/Algorithms/Matching/MatchReplace.swift b/Sources/_StringProcessing/Algorithms/Matching/MatchReplace.swift
index 74ab48839..82ca00797 100644
--- a/Sources/_StringProcessing/Algorithms/Matching/MatchReplace.swift
+++ b/Sources/_StringProcessing/Algorithms/Matching/MatchReplace.swift
@@ -122,6 +122,7 @@ extension RangeReplaceableCollection where SubSequence == Substring {
   ///   sequence matching `regex` to replace. Default is `Int.max`.
   /// - Returns: A new collection in which all occurrences of subsequence
   /// matching `regex` are replaced by `replacement`.
+  @available(SwiftStdlib 5.7, *)
   public func replacing<R: RegexComponent, Replacement: Collection>(
     _ regex: R,
     with replacement: (Regex<R.Output>.Match) throws -> Replacement,
@@ -157,6 +158,7 @@ extension RangeReplaceableCollection where SubSequence == Substring {
   ///   sequence matching `regex` to replace. Default is `Int.max`.
   /// - Returns: A new collection in which all occurrences of subsequence
   /// matching `regex` are replaced by `replacement`.
+  @available(SwiftStdlib 5.7, *)
   public func replacing<R: RegexComponent, Replacement: Collection>(
     _ regex: R,
     with replacement: (Regex<R.Output>.Match) throws -> Replacement,
@@ -177,6 +179,7 @@ extension RangeReplaceableCollection where SubSequence == Substring {
   ///   including captures, and returns a replacement collection.
   ///   - maxReplacements: A number specifying how many occurrences of the
   ///   sequence matching `regex` to replace. Default is `Int.max`.
+  @available(SwiftStdlib 5.7, *)
   public mutating func replace<R: RegexComponent, Replacement: Collection>(
     _ regex: R,
     with replacement: (Regex<R.Output>.Match) throws -> Replacement,
diff --git a/Sources/_StringProcessing/Regex/AnyRegexOutput.swift b/Sources/_StringProcessing/Regex/AnyRegexOutput.swift
index bd0fc47c9..ea9659faf 100644
--- a/Sources/_StringProcessing/Regex/AnyRegexOutput.swift
+++ b/Sources/_StringProcessing/Regex/AnyRegexOutput.swift
@@ -38,6 +38,7 @@ extension Regex.Match where Output == AnyRegexOutput {
 }
 
 /// A type-erased regex output
+@available(SwiftStdlib 5.7, *)
 public struct AnyRegexOutput {
   let input: String
   fileprivate let _elements: [ElementRepresentation]
diff --git a/Sources/_StringProcessing/Regex/Core.swift b/Sources/_StringProcessing/Regex/Core.swift
index 96d0f3a68..b77ee7ece 100644
--- a/Sources/_StringProcessing/Regex/Core.swift
+++ b/Sources/_StringProcessing/Regex/Core.swift
@@ -13,6 +13,7 @@ import _RegexParser
 
 
 /// A type that represents a regular expression.
+@available(SwiftStdlib 5.7, *)
 public protocol RegexComponent {
   associatedtype Output
   var regex: Regex<Output> { get }
@@ -25,6 +26,7 @@ public protocol RegexComponent {
 ///     print(match.0) // "axb"
 ///     print(match.1) // "x"
 ///
+@available(SwiftStdlib 5.7, *)
 public struct Regex<Output>: RegexComponent {
   let program: Program
 
diff --git a/Sources/_StringProcessing/Regex/DSLConsumers.swift b/Sources/_StringProcessing/Regex/DSLConsumers.swift
index 8d64f8355..8bca244c2 100644
--- a/Sources/_StringProcessing/Regex/DSLConsumers.swift
+++ b/Sources/_StringProcessing/Regex/DSLConsumers.swift
@@ -9,6 +9,7 @@
 //
 //===----------------------------------------------------------------------===//
 
+@available(SwiftStdlib 5.7, *)
 public protocol CustomRegexComponent: RegexComponent {
   func match(
     _ input: String,
diff --git a/Sources/_StringProcessing/Regex/DSLTree.swift b/Sources/_StringProcessing/Regex/DSLTree.swift
index f37505cb4..6ae4804e5 100644
--- a/Sources/_StringProcessing/Regex/DSLTree.swift
+++ b/Sources/_StringProcessing/Regex/DSLTree.swift
@@ -12,6 +12,7 @@
 import _RegexParser
 
 @_spi(RegexBuilder)
+@available(SwiftStdlib 5.7, *)
 public struct DSLTree {
   var root: Node
   var options: Options?
@@ -162,6 +163,7 @@ extension DSLTree {
 
 // CollectionConsumer
 @_spi(RegexBuilder)
+@available(SwiftStdlib 5.7, *)
 public typealias _ConsumerInterface = (
   String, Range<String.Index>
 ) throws -> String.Index?
@@ -169,12 +171,14 @@ public typealias _ConsumerInterface = (
 // Type producing consume
 // TODO: better name
 @_spi(RegexBuilder)
+@available(SwiftStdlib 5.7, *)
 public typealias _MatcherInterface = (
   String, String.Index, Range<String.Index>
 ) throws -> (String.Index, Any)?
 
 // Character-set (post grapheme segmentation)
 @_spi(RegexBuilder)
+@available(SwiftStdlib 5.7, *)
 public typealias _CharacterPredicateInterface = (
   (Character) -> Bool
 )
@@ -375,6 +379,7 @@ extension DSLTree.Node {
 }
 
 @_spi(RegexBuilder)
+@available(SwiftStdlib 5.7, *)
 public struct ReferenceID: Hashable, Equatable {
   private static var counter: Int = 0
   var base: Int
@@ -386,6 +391,7 @@ public struct ReferenceID: Hashable, Equatable {
 }
 
 @_spi(RegexBuilder)
+@available(SwiftStdlib 5.7, *)
 public struct CaptureTransform: Hashable, CustomStringConvertible {
   public enum Closure {
     case failable((Substring) throws -> Any?)
diff --git a/Sources/_StringProcessing/_CharacterClassModel.swift b/Sources/_StringProcessing/_CharacterClassModel.swift
index e184689f1..0c45d2b6c 100644
--- a/Sources/_StringProcessing/_CharacterClassModel.swift
+++ b/Sources/_StringProcessing/_CharacterClassModel.swift
@@ -16,6 +16,7 @@ import _RegexParser
 // of parsing or to store in an AST
 
 @_spi(RegexBuilder)
+@available(SwiftStdlib 5.7, *)
 public struct _CharacterClassModel: Hashable {
   /// The actual character class to match.
   var cc: Representation
diff --git a/Tests/RegexBuilderTests/AlgorithmsTests.swift b/Tests/RegexBuilderTests/AlgorithmsTests.swift
index 7625af385..fed584ff7 100644
--- a/Tests/RegexBuilderTests/AlgorithmsTests.swift
+++ b/Tests/RegexBuilderTests/AlgorithmsTests.swift
@@ -13,6 +13,7 @@ import XCTest
 import _StringProcessing
 @testable import RegexBuilder
 
+@available(SwiftStdlib 5.7, *)
 class RegexConsumerTests: XCTestCase {
   // FIXME: enable this test when we update the return type of `matches(of:)`
   // when SE-0346 is available