diff --git a/lld/COFF/DebugTypes.cpp b/lld/COFF/DebugTypes.cpp
--- a/lld/COFF/DebugTypes.cpp
+++ b/lld/COFF/DebugTypes.cpp
@@ -63,7 +63,7 @@
       TypeServerSource *tSrc = (TypeServerSource *)it.first->second;
       log("GUID collision between " + file.getFilePath() + " and " +
           tSrc->pdbInputFile->session->getPDBFile().getFilePath());
-      ctx.typeServerSourceMappings.erase(Guid);
+      it.first->second = nullptr;
     }
   }
 
@@ -405,11 +405,14 @@
   const codeview::GUID &tsId = typeServerDependency.getGuid();
   StringRef tsPath = typeServerDependency.getName();
 
-  TypeServerSource *tsSrc;
+  TypeServerSource *tsSrc = nullptr;
   auto it = ctx.typeServerSourceMappings.find(tsId);
   if (it != ctx.typeServerSourceMappings.end()) {
     tsSrc = (TypeServerSource *)it->second;
-  } else {
+  }
+
+  // check for nullptr since we insert nullptr if we encounter a collision
+  if (tsSrc == nullptr) {
     // The file failed to load, lookup by name
     PDBInputFile *pdb = PDBInputFile::findFromRecordPath(ctx, tsPath, file);
     if (!pdb)