diff --git a/clang-tools-extra/clangd/index/SymbolCollector.cpp b/clang-tools-extra/clangd/index/SymbolCollector.cpp
--- a/clang-tools-extra/clangd/index/SymbolCollector.cpp
+++ b/clang-tools-extra/clangd/index/SymbolCollector.cpp
@@ -469,7 +469,10 @@
     if (!ObjectID)
       continue;
 
-    // Record the relation.
+    // In a BaseOf relation we must've seen the definition/declaration of base
+    // type.
+    if (!Symbols.find(ID))
+      continue;
     // TODO: There may be cases where the object decl is not indexed for some
     // reason. Those cases should probably be removed in due course, but for
     // now there are two possible ways to handle it: