diff --git a/src/lib.ml b/src/lib.ml
index 663ac43906c..1c951eeef82 100644
--- a/src/lib.ml
+++ b/src/lib.ml
@@ -762,6 +762,10 @@ let rec find_implementation_for db lib ~variants =
       ~f:(fun variant acc ->
         List.rev_append acc
           (Variant.Map.Multi.find available_implementations variant))
+    |> List.sort_uniq ~compare:(fun (a:Lib_info.t) (b:Lib_info.t) ->
+      match Lib_name.compare a.name b.name with
+      | Eq -> Path.compare a.src_dir b.src_dir
+      | x -> x)
     |> fun x -> match x, db.parent with
     | [], None -> Ok None
     | [], Some db -> find_implementation_for db lib ~variants
diff --git a/src/stdune/caml/dune_caml.ml b/src/stdune/caml/dune_caml.ml
index 50c661074bc..e0a3875dc9e 100644
--- a/src/stdune/caml/dune_caml.ml
+++ b/src/stdune/caml/dune_caml.ml
@@ -10,6 +10,7 @@ module Lexing   = Lexing
 module Digest   = Digest
 module StringLabels = StringLabels
 module ListLabels   = ListLabels
+module List   = List
 
 type ('a, 'error) result = ('a, 'error) Result.t =
   | Ok    of 'a
diff --git a/src/stdune/list.ml b/src/stdune/list.ml
index 02b688112aa..f20ad954dcd 100644
--- a/src/stdune/list.ml
+++ b/src/stdune/list.ml
@@ -111,6 +111,9 @@ let sort t ~compare =
 let stable_sort t ~compare =
   stable_sort t ~cmp:(fun a b -> Ordering.to_int (compare a b))
 
+let sort_uniq t ~compare =
+  Dune_caml.List.sort_uniq (fun a b -> Ordering.to_int (compare a b)) t
+
 let rec compare a b ~compare:f : Ordering.t =
   match a, b with
   | [], [] -> Eq
diff --git a/src/stdune/list.mli b/src/stdune/list.mli
index 088f19c3f8a..5ae2cf09dee 100644
--- a/src/stdune/list.mli
+++ b/src/stdune/list.mli
@@ -41,6 +41,7 @@ val destruct_last : 'a t -> ('a list * 'a) option
 
 val        sort : 'a t -> compare:('a -> 'a -> Ordering.t) -> 'a t
 val stable_sort : 'a t -> compare:('a -> 'a -> Ordering.t) -> 'a t
+val   sort_uniq : 'a t -> compare:('a -> 'a -> Ordering.t) -> 'a t
 
 val compare : 'a t -> 'a t -> compare:('a -> 'a -> Ordering.t) -> Ordering.t
 
diff --git a/test/blackbox-tests/test-cases/variants/run.t b/test/blackbox-tests/test-cases/variants/run.t
index 2171b44000a..34063c17084 100644
--- a/test/blackbox-tests/test-cases/variants/run.t
+++ b/test/blackbox-tests/test-cases/variants/run.t
@@ -78,3 +78,7 @@ Solving variant ambiguity by specifying a concrete implementation.
   Entering directory 'variant-with-concrete-impl'
            bar alias default
   hello from lib2.default
+
+Don't fail when the same library is defined in multiple scopes.
+  $ dune build --root same-lib-in-multiple-scopes
+  Entering directory 'same-lib-in-multiple-scopes'
diff --git a/test/blackbox-tests/test-cases/variants/same-lib-in-multiple-scopes/dune b/test/blackbox-tests/test-cases/variants/same-lib-in-multiple-scopes/dune
new file mode 100644
index 00000000000..4b37b50c790
--- /dev/null
+++ b/test/blackbox-tests/test-cases/variants/same-lib-in-multiple-scopes/dune
@@ -0,0 +1,9 @@
+(executable
+  (name exe)
+  (variants unix)
+  (libraries test))
+
+(alias
+ (name default)
+ (action
+  (run ./exe.exe)))
diff --git a/test/blackbox-tests/test-cases/variants/same-lib-in-multiple-scopes/dune-project b/test/blackbox-tests/test-cases/variants/same-lib-in-multiple-scopes/dune-project
new file mode 100644
index 00000000000..ec8c49b51b8
--- /dev/null
+++ b/test/blackbox-tests/test-cases/variants/same-lib-in-multiple-scopes/dune-project
@@ -0,0 +1 @@
+(lang dune 1.9)
\ No newline at end of file
diff --git a/test/blackbox-tests/test-cases/variants/same-lib-in-multiple-scopes/exe.ml b/test/blackbox-tests/test-cases/variants/same-lib-in-multiple-scopes/exe.ml
new file mode 100644
index 00000000000..e69de29bb2d
diff --git a/test/blackbox-tests/test-cases/variants/same-lib-in-multiple-scopes/test/dune-project b/test/blackbox-tests/test-cases/variants/same-lib-in-multiple-scopes/test/dune-project
new file mode 100644
index 00000000000..ec8c49b51b8
--- /dev/null
+++ b/test/blackbox-tests/test-cases/variants/same-lib-in-multiple-scopes/test/dune-project
@@ -0,0 +1 @@
+(lang dune 1.9)
\ No newline at end of file
diff --git a/test/blackbox-tests/test-cases/variants/same-lib-in-multiple-scopes/test/test-unix.opam b/test/blackbox-tests/test-cases/variants/same-lib-in-multiple-scopes/test/test-unix.opam
new file mode 100644
index 00000000000..e69de29bb2d
diff --git a/test/blackbox-tests/test-cases/variants/same-lib-in-multiple-scopes/test/test.opam b/test/blackbox-tests/test-cases/variants/same-lib-in-multiple-scopes/test/test.opam
new file mode 100644
index 00000000000..e69de29bb2d
diff --git a/test/blackbox-tests/test-cases/variants/same-lib-in-multiple-scopes/test/unix/dune b/test/blackbox-tests/test-cases/variants/same-lib-in-multiple-scopes/test/unix/dune
new file mode 100644
index 00000000000..c2de3e42a6f
--- /dev/null
+++ b/test/blackbox-tests/test-cases/variants/same-lib-in-multiple-scopes/test/unix/dune
@@ -0,0 +1,5 @@
+(library
+  (name test_unix)
+  (public_name test-unix)
+  (implements test)
+  (variant unix))
diff --git a/test/blackbox-tests/test-cases/variants/same-lib-in-multiple-scopes/test/unix/foo.ml b/test/blackbox-tests/test-cases/variants/same-lib-in-multiple-scopes/test/unix/foo.ml
new file mode 100644
index 00000000000..e69de29bb2d
diff --git a/test/blackbox-tests/test-cases/variants/same-lib-in-multiple-scopes/test/virt/dune b/test/blackbox-tests/test-cases/variants/same-lib-in-multiple-scopes/test/virt/dune
new file mode 100644
index 00000000000..155ccdb47b1
--- /dev/null
+++ b/test/blackbox-tests/test-cases/variants/same-lib-in-multiple-scopes/test/virt/dune
@@ -0,0 +1,4 @@
+(library
+  (name test)
+  (public_name test)
+  (virtual_modules foo))
diff --git a/test/blackbox-tests/test-cases/variants/same-lib-in-multiple-scopes/test/virt/foo.mli b/test/blackbox-tests/test-cases/variants/same-lib-in-multiple-scopes/test/virt/foo.mli
new file mode 100644
index 00000000000..e69de29bb2d