diff --git a/test/ParseableInterface/ModuleCache/prebuilt-module-cache-root.swift b/test/ParseableInterface/ModuleCache/prebuilt-module-cache-root.swift
new file mode 100644
index 00000000000..02a37ce43b7
--- /dev/null
+++ b/test/ParseableInterface/ModuleCache/prebuilt-module-cache-root.swift
@@ -0,0 +1,28 @@
+// RUN: %empty-directory(%t)
+
+// -- construct prebuilt
+// RUN: %empty-directory(%t/prebuilt-cache)
+// RUN: not %target-swift-frontend -typecheck -parse-stdlib -module-cache-path %t/MCP -sdk %S/Inputs -I %S/Inputs/prebuilt-module-cache/ -prebuilt-module-cache-path %t/prebuilt-cache %s 2>&1 | %FileCheck -check-prefix=FROM-INTERFACE %s
+
+// -- generate a manual prebuilt
+// RUN: %empty-directory(%t/MCP)
+// RUN: sed -e 's/FromInterface/FromPrebuilt/g' %S/Inputs/prebuilt-module-cache/Lib.swiftinterface | tr -d '\r' | %target-swift-frontend -parse-stdlib -module-cache-path %t/MCP -emit-module-path %t/prebuilt-cache/Lib.swiftmodule - -module-name Lib
+// RUN: not %target-swift-frontend -typecheck -parse-stdlib -module-cache-path %t/MCP -sdk %S/Inputs -I %S/Inputs/prebuilt-module-cache/ -prebuilt-module-cache-path %t/prebuilt-cache %s 2>&1 | %FileCheck -check-prefix=FROM-PREBUILT %s
+// -- ensure we installed a forwarding module
+// RUN: %{python} %S/Inputs/check-is-forwarding-module.py %t/MCP/Lib-*.swiftmodule
+
+// -- ensure that the search path is in the root
+// RUN: not %target-swift-frontend -typecheck -parse-stdlib -module-cache-path %t/MCP -sdk / -I %S/Inputs/prebuilt-module-cache/ -prebuilt-module-cache-path %t/prebuilt-cache %s 2>&1 | %FileCheck -check-prefix=FROM-PREBUILT %s
+
+// This test is not supported on Windows since the root is not / but rather a
+// drive letter followed by a colon.
+// UNSUPPORTED: OS=windows-msvc
+
+import Lib
+
+struct X {}
+let _: X = Lib.testValue
+
+// FROM-INTERFACE: [[@LINE-2]]:16: error: cannot convert value of type 'FromInterface' to specified type 'X'
+// FROM-PREBUILT: [[@LINE-3]]:16: error: cannot convert value of type 'FromPrebuilt' to specified type 'X'
+
diff --git a/test/ParseableInterface/ModuleCache/prebuilt-module-cache.swift b/test/ParseableInterface/ModuleCache/prebuilt-module-cache.swift
index 93988839b8b..cbf32dffd4d 100644
--- a/test/ParseableInterface/ModuleCache/prebuilt-module-cache.swift
+++ b/test/ParseableInterface/ModuleCache/prebuilt-module-cache.swift
@@ -21,7 +21,6 @@
 // RUN: not %target-swift-frontend -typecheck -parse-stdlib -module-cache-path %t/MCP -sdk %S/Inputs -I %S/Inputs/prebuilt-module-cache/ -prebuilt-module-cache-path %t/prebuilt-cache %s 2>&1 | %FileCheck -check-prefix=FROM-PREBUILT %s
 // RUN: not %target-swift-frontend -typecheck -parse-stdlib -module-cache-path %t/MCP -sdk %S//Inputs -I %S/Inputs/prebuilt-module-cache/ -prebuilt-module-cache-path %t/prebuilt-cache %s 2>&1 | %FileCheck -check-prefix=FROM-PREBUILT %s
 // RUN: not %target-swift-frontend -typecheck -parse-stdlib -module-cache-path %t/MCP -sdk %S/Inputs/prebuilt-module-cache -I %S/Inputs/prebuilt-module-cache/ -prebuilt-module-cache-path %t/prebuilt-cache %s 2>&1 | %FileCheck -check-prefix=FROM-PREBUILT %s
-// RUN: not %target-swift-frontend -typecheck -parse-stdlib -module-cache-path %t/MCP -sdk / -I %S/Inputs/prebuilt-module-cache/ -prebuilt-module-cache-path %t/prebuilt-cache %s 2>&1 | %FileCheck -check-prefix=FROM-PREBUILT %s
 
 // RUN: not %target-swift-frontend -typecheck -parse-stdlib -module-cache-path %t/MCP -sdk %S/Inputs/p -I %S/Inputs/prebuilt-module-cache/ -prebuilt-module-cache-path %t/prebuilt-cache %s 2>&1 | %FileCheck -check-prefix=FROM-INTERFACE %s
 // RUN: not %target-swift-frontend -typecheck -parse-stdlib -module-cache-path %t/MCP -sdk %S/garbage-path -I %S/Inputs/prebuilt-module-cache/ -prebuilt-module-cache-path %t/prebuilt-cache %s 2>&1 | %FileCheck -check-prefix=FROM-INTERFACE %s