diff --git a/bin/alias.ml b/bin/alias.ml
index 02ec8b105be..612b773a7e4 100644
--- a/bin/alias.ml
+++ b/bin/alias.ml
@@ -18,7 +18,8 @@ let in_dir ~name ~recursive ~contexts dir =
   let checked = Util.check_path contexts dir in
   match checked with
   | External _ ->
-    User_error.raise [ Pp.textf "@@ on the command line must be followed by a relative path" ]
+    User_error.raise
+      [ Pp.textf "@@ on the command line must be followed by a relative path" ]
   | In_source_dir dir ->
     { dir
     ; recursive
diff --git a/src/scope.ml b/src/scope.ml
index 65d25589544..1a3173d4a44 100644
--- a/src/scope.ml
+++ b/src/scope.ml
@@ -92,14 +92,13 @@ module DB = struct
       |> Dune_project.Name.Map.of_list
       |> function
       | Ok x -> x
-      | Error (_name, project1, project2) ->
-        let to_dyn (project : Dune_project.t) =
-          Dyn.Encoder.(pair Dune_project.Name.to_dyn Path.Source.to_dyn)
-            (Dune_project.name project, Dune_project.root project)
-        in
-        Code_error.raise "Scope.DB.create got two projects with the same name"
-          [ "project1", to_dyn project1
-          ; "project2", to_dyn project2
+      | Error (name, project1, project2) ->
+        let loc = Loc.in_file (Path.source (Dune_project.file project1)) in
+        let name = Dune_project.Name.to_string_hum name in
+        let dup_path = Path.source (Dune_project.file project2) in
+        User_error.raise ~loc
+          [ Pp.textf "Project %s is already defined in %s"
+              name (Path.to_string_maybe_quoted dup_path)
           ]
     in
     let libs_by_project_name =
diff --git a/test/blackbox-tests/dune.inc b/test/blackbox-tests/dune.inc
index 1184489a0d6..30066b08617 100644
--- a/test/blackbox-tests/dune.inc
+++ b/test/blackbox-tests/dune.inc
@@ -303,6 +303,14 @@
    test-cases/duplicate-c-cxx-obj
    (progn (run %{exe:cram.exe} -test run.t) (diff? run.t run.t.corrected)))))
 
+(alias
+ (name duplicate-project-names)
+ (deps (package dune) (source_tree test-cases/duplicate-project-names))
+ (action
+  (chdir
+   test-cases/duplicate-project-names
+   (progn (run %{exe:cram.exe} -test run.t) (diff? run.t run.t.corrected)))))
+
 (alias
  (name duplicate-target-no-loc)
  (deps (package dune) (source_tree test-cases/duplicate-target-no-loc))
@@ -1631,6 +1639,7 @@
   (alias dup-fields)
   (alias duplicate-c-cxx)
   (alias duplicate-c-cxx-obj)
+  (alias duplicate-project-names)
   (alias duplicate-target-no-loc)
   (alias embed-jbuild)
   (alias enabled_if)
@@ -1823,6 +1832,7 @@
   (alias dup-fields)
   (alias duplicate-c-cxx)
   (alias duplicate-c-cxx-obj)
+  (alias duplicate-project-names)
   (alias duplicate-target-no-loc)
   (alias embed-jbuild)
   (alias enabled_if)
diff --git a/test/blackbox-tests/test-cases/duplicate-project-names/a/dune-project b/test/blackbox-tests/test-cases/duplicate-project-names/a/dune-project
new file mode 100644
index 00000000000..1e9cbae5463
--- /dev/null
+++ b/test/blackbox-tests/test-cases/duplicate-project-names/a/dune-project
@@ -0,0 +1,2 @@
+(lang dune 1.11)
+(name foo)
diff --git a/test/blackbox-tests/test-cases/duplicate-project-names/b/dune-project b/test/blackbox-tests/test-cases/duplicate-project-names/b/dune-project
new file mode 100644
index 00000000000..1e9cbae5463
--- /dev/null
+++ b/test/blackbox-tests/test-cases/duplicate-project-names/b/dune-project
@@ -0,0 +1,2 @@
+(lang dune 1.11)
+(name foo)
diff --git a/test/blackbox-tests/test-cases/duplicate-project-names/run.t b/test/blackbox-tests/test-cases/duplicate-project-names/run.t
new file mode 100644
index 00000000000..3fa656ecb50
--- /dev/null
+++ b/test/blackbox-tests/test-cases/duplicate-project-names/run.t
@@ -0,0 +1,5 @@
+Duplicate project names are currently not allowed:
+  $ dune build @all
+  File "b/dune-project", line 1, characters 0-0:
+  Error: Project foo is already defined in a/dune-project
+  [1]