diff --git a/lld/COFF/DebugTypes.cpp b/lld/COFF/DebugTypes.cpp
--- a/lld/COFF/DebugTypes.cpp
+++ b/lld/COFF/DebugTypes.cpp
@@ -34,6 +34,10 @@
 using namespace lld;
 using namespace lld::coff;
 
+static codeview::GUID InvalidGuid{{0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF,
+                                   0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF,
+                                   0xFF, 0xFF}};
+
 namespace {
 class TypeServerIpiSource;
 
@@ -55,9 +59,20 @@
     if (!expectedInfo)
       return;
     Guid = expectedInfo->getGuid();
-    auto it = ctx.typeServerSourceMappings.emplace(Guid, this);
-    assert(it.second);
-    (void)it;
+    // Don't store the PDB in the map here if the Guid just contains
+    // 0xFF since that will lead to many collisions. This happens with
+    // certain Visual Studio versions where the standard library contains
+    // PDB files with broken/invalid Guids. This will just lead to
+    // a path lookup fallback which works fine - but is slower.
+    if (Guid != InvalidGuid) {
+      auto it = ctx.typeServerSourceMappings.emplace(Guid, this);
+      if (!it.second) {
+        TypeServerSource *tSrc = (TypeServerSource *)it.first->second;
+        warn("GUID collision between " + file.getFilePath() + " and " +
+             tSrc->pdbInputFile->session->getPDBFile().getFilePath());
+      }
+      (void)it;
+    }
   }
 
   Error mergeDebugT(TypeMerger *m) override;