diff --git a/Package.swift b/Package.swift
index 40a96045..56e78074 100644
--- a/Package.swift
+++ b/Package.swift
@@ -5,7 +5,7 @@ import class Foundation.ProcessInfo
 
 let package = Package(
     name: "WasmKit",
-    platforms: [.macOS(.v11), .iOS(.v14)],
+    platforms: [.macOS(.v10_13), .iOS(.v12)],
     products: [
         .library(
             name: "WasmKit",
diff --git a/Sources/Spectest/Spectest.swift b/Sources/Spectest/Spectest.swift
index 5c7885ce..2fed3c8f 100644
--- a/Sources/Spectest/Spectest.swift
+++ b/Sources/Spectest/Spectest.swift
@@ -4,6 +4,7 @@ import SystemPackage
 import WasmKit
 
 @main
+@available(macOS 11, *)
 struct Spectest: AsyncParsableCommand {
     @Argument
     var path: String
diff --git a/Sources/WITExtractor/ModuleTranslation.swift b/Sources/WITExtractor/ModuleTranslation.swift
index b08b9249..2a870b2a 100644
--- a/Sources/WITExtractor/ModuleTranslation.swift
+++ b/Sources/WITExtractor/ModuleTranslation.swift
@@ -1,3 +1,4 @@
+@available(macOS 11, *)
 struct ModuleTranslation {
     let diagnostics: DiagnosticCollection
     let typeMapping: TypeMapping
diff --git a/Sources/WITExtractor/SourceSummary.swift b/Sources/WITExtractor/SourceSummary.swift
index d9ca457f..6e783911 100644
--- a/Sources/WITExtractor/SourceSummary.swift
+++ b/Sources/WITExtractor/SourceSummary.swift
@@ -49,6 +49,7 @@ public struct SwiftFunctionSource {
     let name: String
 }
 
+@available(macOS 11, *)
 struct SourceSummaryBuilder {
     let diagnostics: DiagnosticCollection
     let typeMapping: TypeMapping
diff --git a/Sources/WITExtractor/SwiftAPIDigester.swift b/Sources/WITExtractor/SwiftAPIDigester.swift
index f8c42f1e..794776c8 100644
--- a/Sources/WITExtractor/SwiftAPIDigester.swift
+++ b/Sources/WITExtractor/SwiftAPIDigester.swift
@@ -116,6 +116,7 @@ struct SwiftAPIDigester {
     typealias SDKNodeType = SDKNodeInherit<SDKNodeBody, SDKNodeTypeBody>
     typealias SDKNodeTypeNominal = SDKNodeInherit<SDKNodeType, SDKNodeTypeNominalBody>
 
+    @available(macOS 11, *)
     func dumpSDK(moduleName: String, arguments: [String]) throws -> Output {
         var args = [
             "-dump-sdk",
diff --git a/Sources/WITExtractor/TypeMapping.swift b/Sources/WITExtractor/TypeMapping.swift
index 9da4f018..82ad2cb6 100644
--- a/Sources/WITExtractor/TypeMapping.swift
+++ b/Sources/WITExtractor/TypeMapping.swift
@@ -1,3 +1,4 @@
+@available(macOS 11, *)
 struct TypeMapping {
     typealias DeclScope = [SwiftAPIDigester.SDKNodeDecl]
     struct DeclSource {
diff --git a/Sources/WITExtractor/WITExtractor.swift b/Sources/WITExtractor/WITExtractor.swift
index cacc2f0d..504dd612 100644
--- a/Sources/WITExtractor/WITExtractor.swift
+++ b/Sources/WITExtractor/WITExtractor.swift
@@ -31,6 +31,9 @@ public struct WITExtractor {
     }
 
     public func run(moduleName: String) throws -> Output {
+        guard #available(macOS 11, *) else {
+            fatalError("WITExtractor requires macOS 11+")
+        }
         let header = """
             // DO NOT EDIT.
             //
@@ -42,6 +45,7 @@ public struct WITExtractor {
         return output
     }
 
+    @available(macOS 11, *)
     func runWithoutHeader(moduleName: String) throws -> Output {
         let output = try digester.dumpSDK(moduleName: moduleName, arguments: extraDigesterArguments)
         var typeMapping = TypeMapping()
diff --git a/Sources/WITTool/WITTool.swift b/Sources/WITTool/WITTool.swift
index de5148ea..9a7faf9b 100644
--- a/Sources/WITTool/WITTool.swift
+++ b/Sources/WITTool/WITTool.swift
@@ -123,6 +123,10 @@ struct ExtractWIT: ParsableCommand {
     var digesterArgs: [String] = []
 
     func run() throws {
+        guard #available(macOS 11, *) else {
+            fatalError("ExtractWIT requires macOS 11+")
+        }
+
         let extractor = WITExtractor(
             namespace: namespace,
             packageName: packageName,
diff --git a/Sources/WasmKit/Execution/Runtime/Stack.swift b/Sources/WasmKit/Execution/Runtime/Stack.swift
index a77fffb3..a7f96a66 100644
--- a/Sources/WasmKit/Execution/Runtime/Stack.swift
+++ b/Sources/WasmKit/Execution/Runtime/Stack.swift
@@ -157,8 +157,16 @@ struct ValueStack {
 }
 
 extension ValueStack: Sequence {
-    func makeIterator() -> some IteratorProtocol {
-        self.values[..<count].makeIterator()
+    struct Iterator: IteratorProtocol {
+        fileprivate var base: UnsafeMutableBufferPointer<Value>.SubSequence.Iterator
+
+        mutating func next() -> Value? {
+            base.next()
+        }
+    }
+
+    func makeIterator() -> Iterator {
+        Iterator(base: self.values[..<count].makeIterator())
     }
 }
 
@@ -207,8 +215,16 @@ struct FixedSizeStack<Element> {
 }
 
 extension FixedSizeStack: Sequence {
-    func makeIterator() -> some IteratorProtocol<Element> {
-        self.buffer[..<numberOfElements].makeIterator()
+    struct Iterator: IteratorProtocol {
+        fileprivate var base: UnsafeMutableBufferPointer<Element>.SubSequence.Iterator
+
+        mutating func next() -> Element? {
+            base.next()
+        }
+    }
+
+    func makeIterator() -> Iterator {
+        Iterator(base: self.buffer[..<numberOfElements].makeIterator())
     }
 }