diff --git a/llvm/lib/Transforms/IPO/FunctionImport.cpp b/llvm/lib/Transforms/IPO/FunctionImport.cpp
index c57435e284a6..9489f8d699b5 100644
--- a/llvm/lib/Transforms/IPO/FunctionImport.cpp
+++ b/llvm/lib/Transforms/IPO/FunctionImport.cpp
@@ -697,6 +697,14 @@ Expected<bool> FunctionImporter::importFunctions(
       }
     }
 
+#ifndef DEBUG
+    // Note: this can't be done after `renameModuleForThinLTO` as it leaves the
+    // module in a state that does not pass the verifier (for example aliases
+    // pointing to available_externally functions).
+    if (verifyModule(*SrcModule, &errs()))
+      report_fatal_error("Invalid lazy-loaded source module for importing");
+#endif
+
     // Link in the specified functions.
     if (renameModuleForThinLTO(*SrcModule, Index, &GlobalsToImport))
       return true;