diff --git a/Sources/Testing/ExitTests/ExitTest.swift b/Sources/Testing/ExitTests/ExitTest.swift
index aa7bf39ab..57e38e3ec 100644
--- a/Sources/Testing/ExitTests/ExitTest.swift
+++ b/Sources/Testing/ExitTests/ExitTest.swift
@@ -399,7 +399,7 @@ extension ExitTest {
     asTypeAt typeAddress: UnsafeRawPointer,
     withHintAt hintAddress: UnsafeRawPointer? = nil
   ) -> CBool {
-    fatalError("Unimplemented")
+    swt_unreachable()
   }
 }
 
diff --git a/Sources/TestingMacros/ConditionMacro.swift b/Sources/TestingMacros/ConditionMacro.swift
index 9d0c4f15f..c176c96b5 100644
--- a/Sources/TestingMacros/ConditionMacro.swift
+++ b/Sources/TestingMacros/ConditionMacro.swift
@@ -454,9 +454,9 @@ extension ExitTestConditionMacro {
     // early if found.
     guard _diagnoseIssues(with: macro, body: bodyArgumentExpr, in: context) else {
       if Self.isThrowing {
-        return #"{ () async throws -> Testing.ExitTest.Result in Swift.fatalError("Unreachable") }()"#
+        return #"{ () async throws -> Testing.ExitTest.Result in \#(ExprSyntax.unreachable) }()"#
       } else {
-        return #"{ () async -> Testing.ExitTest.Result in Swift.fatalError("Unreachable") }()"#
+        return #"{ () async -> Testing.ExitTest.Result in \#(ExprSyntax.unreachable) }()"#
       }
     }
 
diff --git a/Sources/TestingMacros/ExitTestCapturedValueMacro.swift b/Sources/TestingMacros/ExitTestCapturedValueMacro.swift
index 4bba47c79..bd346bb3b 100644
--- a/Sources/TestingMacros/ExitTestCapturedValueMacro.swift
+++ b/Sources/TestingMacros/ExitTestCapturedValueMacro.swift
@@ -50,7 +50,7 @@ public struct ExitTestBadCapturedValueMacro: ExpressionMacro, Sendable {
     // Diagnose that the type of 'expr' is invalid.
     context.diagnose(.capturedValueMustBeSendableAndCodable(expr, name: nameExpr))
 
-    return #"Swift.fatalError("Unsupported")"#
+    return .unreachable
   }
 }
 
diff --git a/Sources/TestingMacros/Support/Additions/FunctionDeclSyntaxAdditions.swift b/Sources/TestingMacros/Support/Additions/FunctionDeclSyntaxAdditions.swift
index 9b9378283..090cb2375 100644
--- a/Sources/TestingMacros/Support/Additions/FunctionDeclSyntaxAdditions.swift
+++ b/Sources/TestingMacros/Support/Additions/FunctionDeclSyntaxAdditions.swift
@@ -178,3 +178,15 @@ extension FunctionParameterSyntax {
     return baseType.trimmedDescription
   }
 }
+
+// MARK: -
+
+extension ExprSyntax {
+  /// An expression representing an unreachable code path.
+  ///
+  /// Use this expression when a macro will emit an error diagnostic but the
+  /// compiler still requires us to produce a valid expression.
+  static var unreachable: Self {
+    #"Swift.fatalError("Unreachable")"#
+  }
+}
diff --git a/Sources/TestingMacros/Support/ClosureCaptureListParsing.swift b/Sources/TestingMacros/Support/ClosureCaptureListParsing.swift
index 08536aa69..c4266c99f 100644
--- a/Sources/TestingMacros/Support/ClosureCaptureListParsing.swift
+++ b/Sources/TestingMacros/Support/ClosureCaptureListParsing.swift
@@ -41,7 +41,7 @@ struct CapturedValueInfo {
 
   init(_ capture: ClosureCaptureSyntax, in context: some MacroExpansionContext) {
     self.capture = capture
-    self.expression = #"Swift.fatalError("Unsupported")"#
+    self.expression = .unreachable
     self.type = "Swift.Never"
 
     // We don't support capture specifiers at this time.
diff --git a/Sources/TestingMacros/TagMacro.swift b/Sources/TestingMacros/TagMacro.swift
index 624f812cd..01932ef5d 100644
--- a/Sources/TestingMacros/TagMacro.swift
+++ b/Sources/TestingMacros/TagMacro.swift
@@ -22,7 +22,7 @@ public struct TagMacro: PeerMacro, AccessorMacro, Sendable {
   /// This property is used rather than simply returning the empty array in
   /// order to suppress a compiler diagnostic about not producing any accessors.
   private static var _fallbackAccessorDecls: [AccessorDeclSyntax] {
-    [#"get { Swift.fatalError("Unreachable") }"#]
+    [#"get { \#(ExprSyntax.unreachable) }"#]
   }
 
   public static func expansion(