diff --git a/.swift-format b/.swift-format
index 41a022f2627..176687e2845 100644
--- a/.swift-format
+++ b/.swift-format
@@ -13,6 +13,8 @@
         "NoBlockComments": false,
         "OrderedImports": true,
         "UseLetInEveryBoundCaseVariable": false,
-        "UseSynthesizedInitializer": false
+        "UseSynthesizedInitializer": false,
+        "ReturnVoidInsteadOfEmptyTuple": true,
+        "NoVoidReturnOnFunctionSignature": true,
     }
 }
diff --git a/Examples/Sources/MacroExamples/Implementation/Peer/AddAsyncMacro.swift b/Examples/Sources/MacroExamples/Implementation/Peer/AddAsyncMacro.swift
index 923f002c6c4..1ebe01a8a07 100644
--- a/Examples/Sources/MacroExamples/Implementation/Peer/AddAsyncMacro.swift
+++ b/Examples/Sources/MacroExamples/Implementation/Peer/AddAsyncMacro.swift
@@ -42,7 +42,9 @@ public struct AddAsyncMacro: PeerMacro {
     }
 
     // This only makes sense void functions
-    if funcDecl.signature.returnClause?.type.as(IdentifierTypeSyntax.self)?.name.text != "Void" {
+    if let returnClause = funcDecl.signature.returnClause,
+      returnClause.type.as(IdentifierTypeSyntax.self)?.name.text != "Void"
+    {
       throw CustomError.message(
         "@addAsync requires an function that returns void"
       )
diff --git a/Examples/Sources/MacroExamples/Playground/PeerMacrosPlayground.swift b/Examples/Sources/MacroExamples/Playground/PeerMacrosPlayground.swift
index bc5ba242ca1..f4bfaf335fc 100644
--- a/Examples/Sources/MacroExamples/Playground/PeerMacrosPlayground.swift
+++ b/Examples/Sources/MacroExamples/Playground/PeerMacrosPlayground.swift
@@ -17,12 +17,12 @@ func runPeerMacrosPlayground() {
 
   struct MyStruct {
     @AddAsync
-    func c(a: Int, for b: String, _ value: Double, completionBlock: @escaping (Result<String, Error>) -> Void) -> Void {
+    func c(a: Int, for b: String, _ value: Double, completionBlock: @escaping (Result<String, Error>) -> Void) {
       completionBlock(.success("a: \(a), b: \(b), value: \(value)"))
     }
 
     @AddAsync
-    func d(a: Int, for b: String, _ value: Double, completionBlock: @escaping (Bool) -> Void) -> Void {
+    func d(a: Int, for b: String, _ value: Double, completionBlock: @escaping (Bool) -> Void) {
       completionBlock(true)
     }
   }
diff --git a/Examples/Tests/MacroExamples/Implementation/Peer/AddAsyncMacroTests.swift b/Examples/Tests/MacroExamples/Implementation/Peer/AddAsyncMacroTests.swift
index 79178633770..f936f425dd0 100644
--- a/Examples/Tests/MacroExamples/Implementation/Peer/AddAsyncMacroTests.swift
+++ b/Examples/Tests/MacroExamples/Implementation/Peer/AddAsyncMacroTests.swift
@@ -79,6 +79,32 @@ final class AddAsyncMacroTests: XCTestCase {
     )
   }
 
+  func testImplicitVoidResult() {
+    assertMacroExpansion(
+      """
+      @AddAsync
+      func d(a: Int, completionBlock: @escaping (Bool) -> Void) {
+      }
+      """,
+      expandedSource: """
+        func d(a: Int, completionBlock: @escaping (Bool) -> Void) {
+        }
+
+        func d(a: Int) async -> Bool {
+          await withCheckedContinuation { continuation in
+            d(a: a) { returnValue in
+
+              continuation.resume(returning: returnValue)
+            }
+          }
+
+        }
+        """,
+      macros: macros,
+      indentationWidth: .spaces(2)
+    )
+  }
+
   func testExpansionOnStoredPropertyEmitsError() {
     assertMacroExpansion(
       """
@@ -105,18 +131,18 @@ final class AddAsyncMacroTests: XCTestCase {
     )
   }
 
-  func testExpansionOnAsyncFunctionEmitsError() {
+  func testNonVoidResult() {
     assertMacroExpansion(
       """
       struct Test {
         @AddAsync
-        async func sayHello() {
+        func sayHello() -> Int {
         }
       }
       """,
       expandedSource: """
         struct Test {
-          async func sayHello() {
+          func sayHello() -> Int {
           }
         }
         """,
@@ -132,4 +158,50 @@ final class AddAsyncMacroTests: XCTestCase {
       indentationWidth: .spaces(2)
     )
   }
+
+  func testAlreadyAsync() {
+    assertMacroExpansion(
+      """
+      @AddAsync
+      func d(a: Int, completionBlock: @escaping (Bool) -> Void) async {
+      }
+      """,
+      expandedSource: """
+        func d(a: Int, completionBlock: @escaping (Bool) -> Void) async {
+        }
+        """,
+      diagnostics: [
+        DiagnosticSpec(
+          message: "@addAsync requires an non async function",
+          line: 1,
+          column: 1,
+          severity: .error
+        )
+      ],
+      macros: macros,
+      indentationWidth: .spaces(2)
+    )
+  }
+
+  func testNoCompletionHandler() {
+    assertMacroExpansion(
+      """
+      @AddAsync
+      func sayHello(x: Int) {}
+      """,
+      expandedSource: """
+        func sayHello(x: Int) {}
+        """,
+      diagnostics: [
+        DiagnosticSpec(
+          message: "@addAsync requires an function that has a completion handler as last parameter",
+          line: 1,
+          column: 1,
+          severity: .error
+        )
+      ],
+      macros: macros,
+      indentationWidth: .spaces(2)
+    )
+  }
 }
diff --git a/Sources/SwiftParser/IncrementalParseTransition.swift b/Sources/SwiftParser/IncrementalParseTransition.swift
index c2ebb127817..730f5112da0 100644
--- a/Sources/SwiftParser/IncrementalParseTransition.swift
+++ b/Sources/SwiftParser/IncrementalParseTransition.swift
@@ -47,7 +47,7 @@ extension Parser {
 ///
 /// This is also used for testing purposes to ensure incremental reparsing
 /// worked as expected.
-public typealias ReusedNodeCallback = (_ node: Syntax) -> ()
+public typealias ReusedNodeCallback = (_ node: Syntax) -> Void
 
 /// Keeps track of a previously parsed syntax tree and the source edits that
 /// occurred since it was created.
diff --git a/Sources/SwiftSyntax/SourceLocation.swift b/Sources/SwiftSyntax/SourceLocation.swift
index dcca9d2a74f..4cd64d612b9 100644
--- a/Sources/SwiftSyntax/SourceLocation.swift
+++ b/Sources/SwiftSyntax/SourceLocation.swift
@@ -701,7 +701,7 @@ fileprivate extension SyntaxText {
   /// - Returns: The position at the end of the walk.
   func forEachEndOfLine(
     position: AbsolutePosition,
-    body: (AbsolutePosition) -> ()
+    body: (AbsolutePosition) -> Void
   ) -> AbsolutePosition {
     guard let startPtr = buffer.baseAddress else {
       return position
@@ -745,7 +745,7 @@ fileprivate extension RawTriviaPiece {
   /// - Returns: The position at the end of the walk.
   func forEachEndOfLine(
     position: AbsolutePosition,
-    body: (AbsolutePosition) -> ()
+    body: (AbsolutePosition) -> Void
   ) -> AbsolutePosition {
     var position = position
     switch self {
@@ -788,7 +788,7 @@ fileprivate extension RawTriviaPieceBuffer {
   /// - Returns: The position at the end of the walk.
   func forEachEndOfLine(
     position: AbsolutePosition,
-    body: (AbsolutePosition) -> ()
+    body: (AbsolutePosition) -> Void
   ) -> AbsolutePosition {
     var position = position
     for piece in self {
@@ -810,8 +810,8 @@ fileprivate extension RawSyntax {
   /// - Returns: The position at the end of the walk.
   func forEachEndOfLine(
     position: AbsolutePosition,
-    body: (AbsolutePosition) -> (),
-    handleSourceLocationDirective: (_ position: AbsolutePosition, _ rawSyntax: RawSyntax) -> ()
+    body: (AbsolutePosition) -> Void,
+    handleSourceLocationDirective: (_ position: AbsolutePosition, _ rawSyntax: RawSyntax) -> Void
   ) -> AbsolutePosition {
     var position = position
     switch self.rawData.payload {