diff --git a/clang-tools-extra/clangd/index/remote/marshalling/Marshalling.cpp b/clang-tools-extra/clangd/index/remote/marshalling/Marshalling.cpp
--- a/clang-tools-extra/clangd/index/remote/marshalling/Marshalling.cpp
+++ b/clang-tools-extra/clangd/index/remote/marshalling/Marshalling.cpp
@@ -23,6 +23,7 @@
 #include "llvm/ADT/SmallVector.h"
 #include "llvm/ADT/StringRef.h"
 #include "llvm/Support/Error.h"
+#include "llvm/Support/FormatVariadic.h"
 #include "llvm/Support/Path.h"
 #include "llvm/Support/StringSaver.h"
 
@@ -303,7 +304,8 @@
   if (RelativePath.empty())
     return makeStringError("Empty relative path.");
   if (llvm::sys::path::is_absolute(RelativePath))
-    return makeStringError("RelativePath is absolute.");
+    return makeStringError(
+        llvm::formatv("RelativePath '{0}' is absolute.", RelativePath).str());
   llvm::SmallString<256> FullPath = llvm::StringRef(*LocalIndexRoot);
   llvm::sys::path::append(FullPath, RelativePath);
   auto Result = URI::createFile(FullPath);
@@ -316,10 +318,16 @@
   if (!ParsedURI)
     return ParsedURI.takeError();
   if (ParsedURI->scheme() != "file")
-    return makeStringError("Can not use URI schemes other than file.");
+    return makeStringError(
+        llvm::formatv("Can not use URI schemes other than file, given: '{0}'.",
+                      URI)
+            .str());
   llvm::SmallString<256> Result = ParsedURI->body();
   if (!llvm::sys::path::replace_path_prefix(Result, *RemoteIndexRoot, ""))
-    return makeStringError("File path doesn't start with RemoteIndexRoot.");
+    return makeStringError(
+        llvm::formatv("File path '{0}' doesn't start with '{1}'.", Result.str(),
+                      *RemoteIndexRoot)
+            .str());
   // Make sure the result has UNIX slashes.
   return llvm::sys::path::convert_to_slash(Result,
                                            llvm::sys::path::Style::posix);