diff --git a/Sources/TestingMacros/Support/Additions/WithAttributesSyntaxAdditions.swift b/Sources/TestingMacros/Support/Additions/WithAttributesSyntaxAdditions.swift
index aa778a00c..3c42b6fb3 100644
--- a/Sources/TestingMacros/Support/Additions/WithAttributesSyntaxAdditions.swift
+++ b/Sources/TestingMacros/Support/Additions/WithAttributesSyntaxAdditions.swift
@@ -61,16 +61,17 @@ extension WithAttributesSyntax {
         }.first
 
       var lastPlatformName: TokenSyntax? = nil
-      var asteriskEncountered = false
+      var wildcardEncountered = false
+      let hasWildcard = entries.contains(where: \.isWildcard)
       return entries.compactMap { entry in
         switch entry {
         case let .availabilityVersionRestriction(restriction) where whenKeyword == .introduced:
-          return Availability(attribute: attribute, platformName: restriction.platform, version: restriction.version, message: message)
+          return Availability(attribute: attribute, platformName: restriction.platform, version: restriction.version, mayNeedTrailingWildcard: hasWildcard, message: message)
         case let .token(token):
           if case .identifier = token.tokenKind {
             lastPlatformName = token
-          } else if case let .binaryOperator(op) = token.tokenKind, op == "*" {
-            asteriskEncountered = true
+          } else if entry.isWildcard {
+            wildcardEncountered = true
             // It is syntactically valid to specify a platform name without a
             // version in an availability declaration, and it's used to resolve
             // a custom availability definition specified via the
@@ -81,7 +82,7 @@ extension WithAttributesSyntax {
               return Availability(attribute: attribute, platformName: lastPlatformName, version: nil, message: message)
             }
           } else if case let .keyword(keyword) = token.tokenKind, keyword == whenKeyword {
-            if asteriskEncountered {
+            if wildcardEncountered {
               // Match the "always this availability" construct, i.e.
               // `@available(*, deprecated)` and `@available(*, unavailable)`.
               return Availability(attribute: attribute, platformName: lastPlatformName, version: nil, message: message)
@@ -144,3 +145,13 @@ extension AttributeSyntax {
       .joined()
   }
 }
+
+extension AvailabilityArgumentSyntax.Argument {
+  var isWildcard: Bool {
+    if case let .token(token) = self,
+       case let .binaryOperator(op) = token.tokenKind, op == "*" {
+      return true
+    }
+    return false
+  }
+}
diff --git a/Sources/TestingMacros/Support/AvailabilityGuards.swift b/Sources/TestingMacros/Support/AvailabilityGuards.swift
index deb3a0f8b..93451170c 100644
--- a/Sources/TestingMacros/Support/AvailabilityGuards.swift
+++ b/Sources/TestingMacros/Support/AvailabilityGuards.swift
@@ -24,6 +24,10 @@ struct Availability {
   /// The platform version, such as 1.2.3, if any.
   var version: VersionTupleSyntax?
 
+  /// Whether or not this availability attribute may need a trailing wildcard
+  /// (`*`) when it is expanded into `@available()` or `#available()`.
+  var mayNeedTrailingWildcard = true
+
   /// The `message` argument to the attribute, if any.
   var message: SimpleStringLiteralExprSyntax?
 
@@ -70,13 +74,14 @@ private func _createAvailabilityTraitExpr(
     "(\(literal: components.major), \(literal: components.minor), \(literal: components.patch))"
   } ?? "nil"
   let message = availability.message.map(\.trimmed).map(ExprSyntax.init) ?? "nil"
+  let trailingWildcard = availability.mayNeedTrailingWildcard ? ", *" : ""
   let sourceLocationExpr = createSourceLocationExpr(of: availability.attribute, context: context)
 
   switch (whenKeyword, availability.isSwift) {
   case (.introduced, false):
     return """
     .__available(\(literal: availability.platformName!.textWithoutBackticks), introduced: \(version), message: \(message), sourceLocation: \(sourceLocationExpr)) {
-      if #available(\(availability.platformVersion!), *) {
+      if #available(\(availability.platformVersion!)\(raw: trailingWildcard)) {
         return true
       }
       return false
@@ -207,8 +212,8 @@ func createSyntaxNode(
   do {
     let availableExprs: [ExprSyntax] = decl.availability(when: .introduced).lazy
       .filter { !$0.isSwift }
-      .compactMap(\.platformVersion)
-      .map { "#available(\($0), *)" }
+      .compactMap { ($0.platformVersion, $0.mayNeedTrailingWildcard ? ", *" : "") }
+      .map { "#available(\($0.0)\(raw: $0.1))" }
     if !availableExprs.isEmpty {
       let conditionList = ConditionElementListSyntax {
         for availableExpr in availableExprs {
diff --git a/Tests/TestingMacrosTests/TestDeclarationMacroTests.swift b/Tests/TestingMacrosTests/TestDeclarationMacroTests.swift
index b65a6a62e..aec6d2c10 100644
--- a/Tests/TestingMacrosTests/TestDeclarationMacroTests.swift
+++ b/Tests/TestingMacrosTests/TestDeclarationMacroTests.swift
@@ -415,7 +415,12 @@ struct TestDeclarationMacroTests {
         [
           #"#if os(moofOS)"#,
           #".__available("moofOS", obsoleted: nil, message: "Moof!", "#,
-        ]
+        ],
+      #"@available(customAvailabilityDomain) @Test func f() {}"#:
+        [
+          #".__available("customAvailabilityDomain", introduced: nil, "#,
+          #"guard #available (customAvailabilityDomain) else"#,
+        ],
     ]
   )
   func availabilityAttributeCapture(input: String, expectedOutputs: [String]) throws {