diff --git a/test/Serialization/Inputs/nested-type-with-overlay/overlay.swift b/test/Serialization/Inputs/nested-type-with-overlay/overlay.swift
index 72f831e10f77..754423baa423 100644
--- a/test/Serialization/Inputs/nested-type-with-overlay/overlay.swift
+++ b/test/Serialization/Inputs/nested-type-with-overlay/overlay.swift
@@ -8,3 +8,13 @@ extension Base {
 }
 
 public var shadowedFromSwift = Base.NestedAndShadowed(dummy: ())
+
+public struct CustomError {
+  public struct Code : RawRepresentable {
+    public let rawValue: Int
+
+    public init(rawValue: Int) {
+      self.rawValue = rawValue
+    }
+  }
+}
diff --git a/test/Serialization/nested-type-with-overlay.swift b/test/Serialization/nested-type-with-overlay.swift
index e2c2f36cb042..4b83de9c05b7 100644
--- a/test/Serialization/nested-type-with-overlay.swift
+++ b/test/Serialization/nested-type-with-overlay.swift
@@ -8,8 +8,8 @@
 
 // REQUIRES: asserts
 
-// CHECK: 3 Serialization - # of nested types resolved without full lookup
-// Unfortunately this isn't 4 because of the shadowed nested type from Clang.
+// CHECK: 4 Serialization - # of nested types resolved without full lookup
+// Unfortunately this isn't 5 because of the shadowed nested type from Clang.
 
 import HasOverlay
 
@@ -20,3 +20,9 @@ public func resolveNestedTypes(
 
 public var shadowedFromClang = getShadowedFromClang()
 public var shadowedFromSwift = HasOverlay.shadowedFromSwift
+
+extension CustomError.Code {
+  public static var failedSuccessfully: CustomError.Code {
+    return CustomError.Code(rawValue: -9999)
+  }
+}