diff --git a/clang/test/VFS/Inputs/vfsoverlay-root-relative.yaml b/clang/test/VFS/Inputs/vfsoverlay-root-relative.yaml
new file mode 100644
--- /dev/null
+++ b/clang/test/VFS/Inputs/vfsoverlay-root-relative.yaml
@@ -0,0 +1,17 @@
+{
+  'version': 0,
+  'fallthrough': true,
+  'overlay-relative': true,
+  'roots': [
+    { 'name': 'virtual',
+      'type': 'directory',
+      'contents': [
+        {
+          'external-contents': 'actual_header.h',
+          'type': 'file',
+          'name': 'virtual_header.h',
+        }
+      ]
+    }
+  ]
+}
diff --git a/clang/test/VFS/vfsoverlay-relative-root.c b/clang/test/VFS/vfsoverlay-relative-root.c
new file mode 100644
--- /dev/null
+++ b/clang/test/VFS/vfsoverlay-relative-root.c
@@ -0,0 +1,4 @@
+// RUN: %clang_cc1 -Werror -ivfsoverlay %S/Inputs/vfsoverlay-root-relative.yaml -I virtual -fsyntax-only %s
+
+#include "virtual_header.h"
+
diff --git a/llvm/lib/Support/VirtualFileSystem.cpp b/llvm/lib/Support/VirtualFileSystem.cpp
--- a/llvm/lib/Support/VirtualFileSystem.cpp
+++ b/llvm/lib/Support/VirtualFileSystem.cpp
@@ -1649,10 +1649,17 @@
                                         sys::path::Style::windows_backslash)) {
         path_style = sys::path::Style::windows_backslash;
       } else {
-        assert(NameValueNode && "Name presence should be checked earlier");
-        error(NameValueNode,
-              "entry with relative path at the root level is not discoverable");
-        return nullptr;
+        // Relative VFS root entries are made absolute to the current working
+        // directory, then we can determine the path style from that.
+        auto EC = sys::fs::make_absolute(Name);
+        if (EC) {
+          assert(NameValueNode && "Name presence should be checked earlier");
+          error(NameValueNode,
+                "entry with relative path at the root level is not discoverable");
+          return nullptr;
+        }
+        path_style = sys::path::is_absolute(Name, sys::path::Style::posix) ?
+          sys::path::Style::posix : sys::path::Style::windows_backslash;
       }
     }