diff --git a/lldb/source/Core/SourceManager.cpp b/lldb/source/Core/SourceManager.cpp
--- a/lldb/source/Core/SourceManager.cpp
+++ b/lldb/source/Core/SourceManager.cpp
@@ -696,7 +696,7 @@
 }
 
 void SourceManager::SourceFileCache::AddSourceFile(const FileSP &file_sp) {
-  FileSpec file_spec;
+  FileSpec file_spec = file_sp->GetFileSpec();
   FileCache::iterator pos = m_file_cache.find(file_spec);
   if (pos == m_file_cache.end())
     m_file_cache[file_spec] = file_sp;
diff --git a/lldb/unittests/Core/CMakeLists.txt b/lldb/unittests/Core/CMakeLists.txt
--- a/lldb/unittests/Core/CMakeLists.txt
+++ b/lldb/unittests/Core/CMakeLists.txt
@@ -2,6 +2,7 @@
   CommunicationTest.cpp
   MangledTest.cpp
   RichManglingContextTest.cpp
+  SourceManagerTest.cpp
   StreamCallbackTest.cpp
   UniqueCStringMapTest.cpp
 
diff --git a/lldb/unittests/Core/SourceManagerTest.cpp b/lldb/unittests/Core/SourceManagerTest.cpp
new file mode 100644
--- /dev/null
+++ b/lldb/unittests/Core/SourceManagerTest.cpp
@@ -0,0 +1,48 @@
+//===-- SourceManagerTest.cpp ---------------------------------------------===//
+//
+// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
+// See https://llvm.org/LICENSE.txt for license information.
+// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+//
+//===----------------------------------------------------------------------===//
+
+#include "lldb/Core/SourceManager.h"
+#include "lldb/Host/FileSystem.h"
+#include "gtest/gtest.h"
+
+using namespace lldb;
+using namespace lldb_private;
+
+class SourceFileCache : public ::testing::Test {
+public:
+  void SetUp() override { FileSystem::Initialize(); }
+  void TearDown() override { FileSystem::Terminate(); }
+};
+
+TEST_F(SourceFileCache, FindSourceFileFound) {
+  SourceManager::SourceFileCache cache;
+
+  // Insert: foo
+  FileSpec foo_file_spec("foo");
+  auto foo_file_sp =
+      std::make_shared<SourceManager::File>(foo_file_spec, nullptr);
+  cache.AddSourceFile(foo_file_sp);
+
+  // Query: foo, expect found.
+  FileSpec another_foo_file_spec("foo");
+  ASSERT_EQ(cache.FindSourceFile(another_foo_file_spec), foo_file_sp);
+}
+
+TEST_F(SourceFileCache, FindSourceFileNotFound) {
+  SourceManager::SourceFileCache cache;
+
+  // Insert: foo
+  FileSpec foo_file_spec("foo");
+  auto foo_file_sp =
+      std::make_shared<SourceManager::File>(foo_file_spec, nullptr);
+  cache.AddSourceFile(foo_file_sp);
+
+  // Query: bar, expect not found.
+  FileSpec bar_file_spec("bar");
+  ASSERT_EQ(cache.FindSourceFile(bar_file_spec), nullptr);
+}