diff --git a/lib/Frontend/DiagnosticVerifier.cpp b/lib/Frontend/DiagnosticVerifier.cpp
index 953c0eb27bb77..473f153e4cb0e 100644
--- a/lib/Frontend/DiagnosticVerifier.cpp
+++ b/lib/Frontend/DiagnosticVerifier.cpp
@@ -1289,15 +1289,17 @@ bool DiagnosticVerifier::finishProcessing() {
 
   SmallVector<unsigned, 4> additionalBufferIDs;
   for (auto path : AdditionalFilePaths) {
-    auto bufferID = SM.getIDForBufferIdentifier(path);
+    llvm::SmallString<261> buffer{path};
+    llvm::sys::path::make_preferred(buffer);
+    auto bufferID = SM.getIDForBufferIdentifier(buffer);
     if (!bufferID) {
       // Still need to scan this file for expectations.
-      auto result = SM.getFileSystem()->getBufferForFile(path);
+      auto result = SM.getFileSystem()->getBufferForFile(buffer);
       if (!result) {
         auto message = SM.GetMessage(
            SourceLoc(), llvm::SourceMgr::DiagKind::DK_Error,
            llvm::Twine("unable to open file in '-verify-additional-file ") +
-           path + "': " + result.getError().message(), {}, {});
+           buffer + "': " + result.getError().message(), {}, {});
         printDiagnostic(message);
         Result.HadError |= true;
         continue;
diff --git a/test/ModuleInterface/BadStdlib.swiftinterface b/test/ModuleInterface/BadStdlib.swiftinterface
index 9b353dc80a1cd..8f05b5e87dc80 100644
--- a/test/ModuleInterface/BadStdlib.swiftinterface
+++ b/test/ModuleInterface/BadStdlib.swiftinterface
@@ -14,6 +14,3 @@
 import ClangMod
 
 public func useHasPointer(_: HasPointer)
-
-// FIXME: https://github.com/apple/swift/issues/56844
-// UNSUPPORTED: OS=windows-msvc