Index: clang/lib/Lex/HeaderSearch.cpp
===================================================================
--- clang/lib/Lex/HeaderSearch.cpp
+++ clang/lib/Lex/HeaderSearch.cpp
@@ -172,6 +172,10 @@
 std::string HeaderSearch::getCachedModuleFileName(Module *Module) {
   const FileEntry *ModuleMap =
       getModuleMap().getModuleMapFileForUniquing(Module);
+  // The ModuleMap maybe a nullptr, when we load a cached C++ module without
+  // *.modulemap file. In this case, just return an empty string.
+  if (ModuleMap == nullptr)
+    return {};
   return getCachedModuleFileName(Module->Name, ModuleMap->getName());
 }
 
Index: clang/test/Modules/implicit-module-with-missing-path.cpp
===================================================================
--- /dev/null
+++ clang/test/Modules/implicit-module-with-missing-path.cpp
@@ -0,0 +1,12 @@
+// This tests that the compiler wouldn't crash if the module path misses
+
+// RUN: rm -rf %t
+// RUN: mkdir -p %t/subdir
+// RUN: echo "export module C;" >> %t/subdir/C.cppm
+// RUN: echo -e "export module B;\nimport C;" >> %t/B.cppm
+// RUN: %clang_cc1 -std=c++20 -emit-module-interface %t/subdir/C.cppm -o %t/subdir/C.pcm
+// RUN: %clang_cc1 -std=c++20 -emit-module-interface -fprebuilt-module-path=%t/subdir %t/B.cppm -o %t/B.pcm
+// RUN: %clang_cc1 -std=c++20 -fprebuilt-module-path=%t %s -fsyntax-only -verify
+
+import B;
+import C; // expected-error {{module 'C' is needed but has not been provided, and implicit use of module files is disabled}}