--- a/build/clang-plugin/mozsearch-plugin/MozsearchIndexer.cpp
+++ b/build/clang-plugin/mozsearch-plugin/MozsearchIndexer.cpp
@@ -95,17 +95,21 @@ struct FileInfo {
       // We're in the objdir, so we are probably a generated header
       // We use the escape character to indicate the objdir nature.
       // Note that output also has the `/' already placed
       Interesting = true;
       Realname.replace(0, Objdir.length(), GENERATED);
       return;
     }
 
-    Interesting = Rname.compare(0, Srcdir.length(), Srcdir) == 0;
+    // Empty filenames can get turned into Srcdir when they are resolved as
+    // absolute paths, so we should exclude files that are exactly equal to
+    // Srcdir or anything outside Srcdir.
+    Interesting = (Rname.length() > Srcdir.length()) &&
+                  (Rname.compare(0, Srcdir.length(), Srcdir) == 0);
     if (Interesting) {
       // Remove the trailing `/' as well.
       Realname.erase(0, Srcdir.length() + 1);
     }
   }
   std::string Realname;
   std::vector<std::string> Output;
   bool Interesting;
@@ -171,19 +175,26 @@ private:
     FileID Id = SM.getFileID(Loc);
 
     std::map<FileID, std::unique_ptr<FileInfo>>::iterator It;
     It = FileMap.find(Id);
     if (It == FileMap.end()) {
       // We haven't seen this file before. We need to make the FileInfo
       // structure information ourselves
       std::string Filename = SM.getFilename(Loc);
-      std::string Absolute = getAbsolutePath(Filename);
-      if (Absolute.empty()) {
-        Absolute = Filename;
+      std::string Absolute;
+      // If Loc is a macro id rather than a file id, it Filename might be
+      // empty. Also for some types of file locations that are clang-internal
+      // like "<scratch>" it can return an empty Filename. In these cases we
+      // want to leave Absolute as empty.
+      if (!Filename.empty()) {
+        Absolute = getAbsolutePath(Filename);
+        if (Absolute.empty()) {
+          Absolute = Filename;
+        }
       }
       std::unique_ptr<FileInfo> Info = llvm::make_unique<FileInfo>(Absolute);
       It = FileMap.insert(std::make_pair(Id, std::move(Info))).first;
     }
     return It->second.get();
   }
 
   // Helpers for processing declarations