diff --git a/CHANGES.md b/CHANGES.md
index 26b274947..f171f3835 100644
--- a/CHANGES.md
+++ b/CHANGES.md
@@ -14,6 +14,8 @@ UNRELEASED
     - Perform incremental indexation of the buffer when typing. (#1777)
     - `merlin-lib.commands`: Add a `find_command_opt`` alternative to
       `find_command` that does not raise (#1778)
+    - Prevent uid clashes by not returning PWO for defs located in the current
+      interface file (#1781)
   + editor modes
     - emacs: add basic support for project-wide occurrences (#1766)
     - vim: add basic support for project-wide occurrences (#1767, @Julow)
diff --git a/src/analysis/occurrences.ml b/src/analysis/occurrences.ml
index 1a7aad559..9e3458476 100644
--- a/src/analysis/occurrences.ml
+++ b/src/analysis/occurrences.ml
@@ -117,6 +117,11 @@ let get_buffer_locs result uid =
     (Mtyper.get_index result)
     Lid_set.empty
 
+let is_in_interface (config : Mconfig.t) (loc : Warnings.loc) =
+  let extension = Filename.extension loc.loc_start.pos_fname in
+  List.exists config.merlin.suffixes
+    ~f:(fun (_impl, intf) -> String.equal extension intf)
+
 let locs_of ~config ~env ~typer_result ~pos ~scope path =
   log ~title:"occurrences" "Looking for occurences of %s (pos: %s)"
     path
@@ -135,10 +140,31 @@ let locs_of ~config ~env ~typer_result ~pos ~scope path =
       (* We are on  a definition / declaration so we look for the node's uid  *)
       let browse = Mbrowse.of_typedtree local_defs in
       let env, node = Mbrowse.leaf_node (Mbrowse.enclosing pos [browse]) in
-      uid_and_loc_of_node env node, scope
+      let node_uid_loc = uid_and_loc_of_node env node in
+      let scope =
+        match node_uid_loc with
+        | Some (_, l) when is_in_interface config l ->
+          (* There is no way to distinguish uids from interfaces from uids of
+             implementations. We fallback on buffer occurrences in that case.
+             TODO: we should be able to improve on that situation when we will be
+             able to distinguish between impl/intf uids and know which declaration
+             are actually linked. *)
+          `Buffer
+        | _ -> scope
+      in
+      node_uid_loc, scope
     | `Found { uid; location; approximated = false; _ } ->
         log ~title:"locs_of" "Found definition uid using locate: %a "
           Logger.fmt (fun fmt -> Shape.Uid.print fmt uid);
+        (* There is no way to distinguish uids from interfaces from uids of
+           implementations. We fallback on buffer occurrences in that case.
+           TODO: we should be able to improve on that situation when we will be
+           able to distinguish between impl/intf uids and know which declaration
+           are actually linked. *)
+        let scope =
+          if is_in_interface config location then `Buffer
+          else scope
+        in
         Some (uid, location), scope
     | `Found { decl_uid; location; approximated = true; _ } ->
         log ~title:"locs_of" "Approx. definition: %a "
@@ -178,7 +204,12 @@ let locs_of ~config ~env ~typer_result ~pos ~scope path =
           Lid_set.filter (fun {loc; _} ->
           (* We ignore external results that concern the current buffer *)
           let file = loc.Location.loc_start.Lexing.pos_fname in
-          if String.equal file current_buffer_path then false
+          let file, buf =
+            match config.merlin.source_root with
+            | Some root -> Filename.concat root file, current_buffer_path
+            | None -> file, config.query.filename
+          in
+          if String.equal file buf then false
           else begin
             (* We ignore external results if their source was modified *)
             let check = Stat_check.check stats ~file in
diff --git a/tests/test-dirs/occurrences/project-wide/mli-vs-ml.t b/tests/test-dirs/occurrences/project-wide/mli-vs-ml.t
new file mode 100644
index 000000000..12e0926dc
--- /dev/null
+++ b/tests/test-dirs/occurrences/project-wide/mli-vs-ml.t
@@ -0,0 +1,86 @@
+  $ cat >main.mli <<'EOF'
+  > type t = unit
+  > val x : t
+  > EOF
+
+  $ cat >main.ml <<'EOF'
+  > let x = ()
+  > type t = unit
+  > EOF
+
+  $ ocamlc -bin-annot -bin-annot-occurrences -c main.mli main.ml
+
+  $ ocaml-index aggregate main.cmti main.cmt
+
+The indexer should not mixup uids from mli and ml files:
+  $ ocaml-index dump project.ocaml-index
+  2 uids:
+  {uid: Main.0; locs: "x": File "main.ml", line 1, characters 4-5
+   uid: Main.1; locs: "t": File "main.ml", line 2, characters 5-6 },
+  0 approx shapes: {}, and shapes for CUS .
+
+Merlin should not mixup uids from mli and ml files:
+  $ $MERLIN single occurrences -scope project -identifier-at 2:8 \
+  > -index-file project.ocaml-index \
+  > -filename main.mli <main.mli
+  {
+    "class": "return",
+    "value": [
+      {
+        "file": "$TESTCASE_ROOT/main.mli",
+        "start": {
+          "line": 1,
+          "col": 5
+        },
+        "end": {
+          "line": 1,
+          "col": 6
+        }
+      },
+      {
+        "file": "$TESTCASE_ROOT/main.mli",
+        "start": {
+          "line": 2,
+          "col": 8
+        },
+        "end": {
+          "line": 2,
+          "col": 9
+        }
+      }
+    ],
+    "notifications": []
+  }
+
+Same when the cursor is at the origin:
+  $ $MERLIN single occurrences -scope project -identifier-at 1:5 \
+  > -index-file project.ocaml-index \
+  > -filename main.mli <main.mli
+  {
+    "class": "return",
+    "value": [
+      {
+        "file": "$TESTCASE_ROOT/main.mli",
+        "start": {
+          "line": 1,
+          "col": 5
+        },
+        "end": {
+          "line": 1,
+          "col": 6
+        }
+      },
+      {
+        "file": "$TESTCASE_ROOT/main.mli",
+        "start": {
+          "line": 2,
+          "col": 8
+        },
+        "end": {
+          "line": 2,
+          "col": 9
+        }
+      }
+    ],
+    "notifications": []
+  }