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 +1,3 @@
+// RUN: %clang_cc1 -Werror -ivfsoverlay %S/Inputs/vfsoverlay-root-relative.yaml -I virtual -fsyntax-only %s
+
+#include "virtual_header.h"
diff --git a/llvm/include/llvm/Support/VirtualFileSystem.h b/llvm/include/llvm/Support/VirtualFileSystem.h
--- a/llvm/include/llvm/Support/VirtualFileSystem.h
+++ b/llvm/include/llvm/Support/VirtualFileSystem.h
@@ -547,6 +547,9 @@
 /// }
 /// \endverbatim
 ///
+/// The roots may be absolute or relative. If relative they will be made
+/// absolute against the current working directory.
+///
 /// All configuration options are optional.
 ///   'case-sensitive': <boolean, default=(true for Posix, false for Windows)>
 ///   'use-external-names': <boolean, default=true>
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 +1649,19 @@
                                         sys::path::Style::windows_backslash)) {
         path_style = sys::path::Style::windows_backslash;
       } else {
-        assert(NameValueNode && "Name presence should be checked earlier");
-        error(NameValueNode,
+        // 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;
+          return nullptr;
+        }
+        path_style = sys::path::is_absolute(Name, sys::path::Style::posix)
+                         ? sys::path::Style::posix
+                         : sys::path::Style::windows_backslash;
       }
     }
 
diff --git a/llvm/unittests/Support/VirtualFileSystemTest.cpp b/llvm/unittests/Support/VirtualFileSystemTest.cpp
--- a/llvm/unittests/Support/VirtualFileSystemTest.cpp
+++ b/llvm/unittests/Support/VirtualFileSystemTest.cpp
@@ -2164,6 +2164,11 @@
 
 TEST_F(VFSFromYAMLTest, RelativePaths) {
   IntrusiveRefCntPtr<DummyFileSystem> Lower(new DummyFileSystem());
+  std::error_code EC;
+  SmallString<128> current_dir;
+  EC = llvm::sys::fs::current_path(current_dir);
+  ASSERT_FALSE(EC);
+
   // Filename at root level without a parent directory.
   IntrusiveRefCntPtr<vfs::FileSystem> FS = getFromYAMLString(
       "{ 'roots': [\n"
@@ -2172,7 +2177,12 @@
       "  }\n"
       "] }",
       Lower);
-  EXPECT_EQ(nullptr, FS.get());
+  ASSERT_TRUE(FS.get() != nullptr);
+  SmallString<128> expected_path_not_in_dir("file-not-in-directory.h");
+  llvm::sys::fs::make_absolute(expected_path_not_in_dir);
+  checkContents(FS->dir_begin(current_dir, EC),
+                {expected_path_not_in_dir});
+
 
   // Relative file path.
   FS = getFromYAMLString("{ 'roots': [\n"
@@ -2181,7 +2191,13 @@
                          "  }\n"
                          "] }",
                          Lower);
-  EXPECT_EQ(nullptr, FS.get());
+  ASSERT_TRUE(FS.get() != nullptr);
+  SmallString<128> expected_path_relative_file_parent("relative/file");
+  SmallString<128> expected_path_relative_file("relative/file/path.h");
+  llvm::sys::fs::make_absolute(expected_path_relative_file_parent);
+  llvm::sys::fs::make_absolute(expected_path_relative_file);
+  checkContents(FS->dir_begin(expected_path_relative_file_parent, EC),
+                {expected_path_relative_file});
 
   // Relative directory path.
   FS = getFromYAMLString(
@@ -2191,9 +2207,15 @@
       "  }\n"
       "] }",
       Lower);
-  EXPECT_EQ(nullptr, FS.get());
+  ASSERT_TRUE(FS.get() != nullptr);
+  SmallString<128> expected_path_relative_dir_parent("relative/directory");
+  SmallString<128> expected_path_relative_dir("relative/directory/path.h");
+  llvm::sys::fs::make_absolute(expected_path_relative_dir_parent);
+  llvm::sys::fs::make_absolute(expected_path_relative_dir);
+  checkContents(FS->dir_begin(expected_path_relative_dir_parent, EC),
+                {expected_path_relative_dir});
 
-  EXPECT_EQ(3, NumDiagnostics);
+  EXPECT_EQ(0, NumDiagnostics);
 }
 
 TEST_F(VFSFromYAMLTest, NonFallthroughDirectoryIteration) {