diff --git a/Sources/TestingMacros/TestDeclarationMacro.swift b/Sources/TestingMacros/TestDeclarationMacro.swift
index 2a4da4e3c..307b1615d 100644
--- a/Sources/TestingMacros/TestDeclarationMacro.swift
+++ b/Sources/TestingMacros/TestDeclarationMacro.swift
@@ -328,7 +328,7 @@ public struct TestDeclarationMacro: PeerMacro, Sendable {
         }
         FunctionParameterSyntax(
           firstName: .wildcardToken(),
-          type: "isolated (any Actor)?" as TypeSyntax,
+          type: "isolated (any _Concurrency.Actor)?" as TypeSyntax,
           defaultValue: InitializerClauseSyntax(value: "Testing.__defaultSynchronousIsolationContext" as ExprSyntax)
         )
       }
diff --git a/Tests/TestingTests/MiscellaneousTests.swift b/Tests/TestingTests/MiscellaneousTests.swift
index 1f18f20a9..b4b12a217 100644
--- a/Tests/TestingTests/MiscellaneousTests.swift
+++ b/Tests/TestingTests/MiscellaneousTests.swift
@@ -139,6 +139,11 @@ struct SendableTests: Sendable {
 @Suite("Named Sendable test type", .hidden)
 struct NamedSendableTests: Sendable {}
 
+// This is meant to help detect unqualified usages of the `Actor` protocol from
+// Swift's `_Concurrency` module in macro expansion code, since it's possible
+// for another module to declare a type with that name.
+private class Actor {}
+
 #if !SWT_NO_GLOBAL_ACTORS
 @Suite(.hidden)
 @MainActor