diff --git a/analysis/src/NewCompletions.ml b/analysis/src/NewCompletions.ml
index bbec85cc9..97e81b5ed 100644
--- a/analysis/src/NewCompletions.ml
+++ b/analysis/src/NewCompletions.ml
@@ -773,7 +773,7 @@ let getItems ~full ~package ~rawOpens ~allFiles ~pos ~parts =
     in
     (* TODO complete the namespaced name too *)
     let localModuleNames =
-      allFiles
+      allFiles |> FileSet.elements
       |> Utils.filterMap (fun name ->
              if Utils.startsWith name suffix && not (String.contains name '-')
              then Some {(emptyDeclared name) with item = FileModule name}
@@ -1148,7 +1148,9 @@ let computeCompletions ~uri ~textOpt ~pos =
         | Some full ->
           let rawOpens = PartialParser.findOpens text offset in
           let package = full.package in
-          let allFiles = package.projectFiles @ package.dependenciesFiles in
+          let allFiles =
+            FileSet.union package.projectFiles package.dependenciesFiles
+          in
           let findItems ~exact parts =
             let items =
               getItems ~full ~package ~rawOpens ~allFiles ~pos ~parts
diff --git a/analysis/src/Packages.ml b/analysis/src/Packages.ml
index d095503b7..7401d71f0 100644
--- a/analysis/src/Packages.ml
+++ b/analysis/src/Packages.ml
@@ -84,8 +84,12 @@ let newBsPackage rootPath =
            Log.log ("Opens from bsconfig: " ^ (opens |> String.concat " "));
            {
              SharedTypes.rootPath;
-             projectFiles = projectFilesAndPaths |> List.map fst;
-             dependenciesFiles = dependenciesFilesAndPaths |> List.map fst;
+             projectFiles =
+               projectFilesAndPaths |> List.map fst
+               |> SharedTypes.FileSet.of_list;
+             dependenciesFiles =
+               dependenciesFilesAndPaths |> List.map fst
+               |> SharedTypes.FileSet.of_list;
              pathsForModule;
              opens;
              namespace;
diff --git a/analysis/src/ProcessCmt.ml b/analysis/src/ProcessCmt.ml
index e5b372827..e13e000bc 100644
--- a/analysis/src/ProcessCmt.ml
+++ b/analysis/src/ProcessCmt.ml
@@ -734,12 +734,12 @@ struct
       else []))
 
   let addFileReference moduleName loc =
-    Hashtbl.replace extra.fileReferences moduleName
-      (loc
-      ::
-      (if Hashtbl.mem extra.fileReferences moduleName then
-       Hashtbl.find extra.fileReferences moduleName
-      else []))
+    let newLocs =
+      match Hashtbl.find_opt extra.fileReferences moduleName with
+      | Some oldLocs -> LocationSet.add loc oldLocs
+      | None -> LocationSet.singleton loc
+    in
+    Hashtbl.replace extra.fileReferences moduleName newLocs
 
   let env = QueryEnv.fromFile Collector.file
 
diff --git a/analysis/src/References.ml b/analysis/src/References.ml
index 9dcc16aa7..f6e1e38fc 100644
--- a/analysis/src/References.ml
+++ b/analysis/src/References.ml
@@ -426,7 +426,7 @@ let forLocalStamp ~full:{file; extra; package} stamp tip =
               maybeLog ("Now checking path " ^ pathToString path);
               let thisModuleName = file.moduleName in
               let externals =
-                package.projectFiles
+                package.projectFiles |> FileSet.elements
                 |> List.filter (fun name -> name <> file.moduleName)
                 |> Utils.filterMap (fun name ->
                        match ProcessCmt.fileForModule ~package name with
@@ -460,7 +460,7 @@ let allReferencesForLocItem ~full:({file; package} as full) locItem =
   match locItem.locType with
   | TopLevelModule moduleName ->
     let otherModulesReferences =
-      package.projectFiles
+      package.projectFiles |> FileSet.elements
       |> Utils.filterMap (fun name ->
              match ProcessCmt.fileForModule ~package name with
              | None -> None
@@ -469,7 +469,7 @@ let allReferencesForLocItem ~full:({file; package} as full) locItem =
              match Hashtbl.find_opt full.extra.fileReferences moduleName with
              | None -> []
              | Some locs ->
-               locs
+               locs |> LocationSet.elements
                |> List.map (fun loc ->
                       (Uri2.fromPath loc.Location.loc_start.pos_fname, [loc])))
       |> List.flatten
diff --git a/analysis/src/SharedTypes.ml b/analysis/src/SharedTypes.ml
index 948996527..4f074194e 100644
--- a/analysis/src/SharedTypes.ml
+++ b/analysis/src/SharedTypes.ml
@@ -200,10 +200,16 @@ type openTracker = {
   mutable used : (path * tip * Location.t) list;
 }
 
+module LocationSet = Set.Make (struct
+  include Location
+
+  let compare loc1 loc2 = compare loc2 loc1 (* polymorphic compare should be OK *)
+end)
+
 type extra = {
   internalReferences : (int, Location.t list) Hashtbl.t;
   externalReferences : (string, (path * tip * Location.t) list) Hashtbl.t;
-  fileReferences : (string, Location.t list) Hashtbl.t;
+  fileReferences : (string, LocationSet.t) Hashtbl.t;
   mutable locItems : locItem list;
   (* This is the "open location", like the location...
      or maybe the >> location of the open ident maybe *)
@@ -213,10 +219,12 @@ type extra = {
 
 type file = string
 
+module FileSet = Set.Make (String)
+
 type package = {
   rootPath : filePath;
-  projectFiles : file list;
-  dependenciesFiles : file list;
+  projectFiles : FileSet.t;
+  dependenciesFiles : FileSet.t;
   pathsForModule : (file, paths) Hashtbl.t;
   namespace : string option;
   opens : string list;