diff --git a/lib/Serialization/ASTReader.cpp b/lib/Serialization/ASTReader.cpp
index c5edca7..9d50f7a 100644
--- a/lib/Serialization/ASTReader.cpp
+++ b/lib/Serialization/ASTReader.cpp
@@ -2976,7 +2976,10 @@
         Data += Len;
         ModuleFile *OM = ModuleMgr.lookup(Name);
         if (!OM) {
-          Error("SourceLocation remap refers to unknown module");
+          std::string Msg =
+              "SourceLocation remap refers to unknown module, cannot find ";
+          Msg.append(Name);
+          Error(Msg);
           return Failure;
         }