diff --git a/CHANGES.md b/CHANGES.md
index 0f9344f1c1..cde92d2fa9 100644
--- a/CHANGES.md
+++ b/CHANGES.md
@@ -10,6 +10,8 @@ unreleased
   + ocaml-index
     - Improve the granularity of index reading by segmenting the marshalization
       of the involved data-structures. (#1889)
+  + test suite
+    - Add a test case illustrating wrong open order proposed in issue #1900. (#1901)
 
 merlin 5.4.1
 ============
diff --git a/tests/test-dirs/dune b/tests/test-dirs/dune
index 6e9db30beb..44b808f2a8 100755
--- a/tests/test-dirs/dune
+++ b/tests/test-dirs/dune
@@ -1,6 +1,6 @@
 (cram
  (applies_to no-escape type-expr environment_on_open locate-type
-   polarity-search)
+   polarity-search issue1900)
  (enabled_if
   (<> %{os_type} Win32)))
 
diff --git a/tests/test-dirs/issue1900.t/a.ml b/tests/test-dirs/issue1900.t/a.ml
new file mode 100644
index 0000000000..bf401c9275
--- /dev/null
+++ b/tests/test-dirs/issue1900.t/a.ml
@@ -0,0 +1 @@
+let x = "test"
diff --git a/tests/test-dirs/issue1900.t/dune b/tests/test-dirs/issue1900.t/dune
new file mode 100644
index 0000000000..fb4894a793
--- /dev/null
+++ b/tests/test-dirs/issue1900.t/dune
@@ -0,0 +1,4 @@
+(executable
+ (name main)
+ (libraries lib)
+ (flags :standard -open Lib))
diff --git a/tests/test-dirs/issue1900.t/dune-project b/tests/test-dirs/issue1900.t/dune-project
new file mode 100644
index 0000000000..37f995d649
--- /dev/null
+++ b/tests/test-dirs/issue1900.t/dune-project
@@ -0,0 +1 @@
+(lang dune 3.0)
diff --git a/tests/test-dirs/issue1900.t/lib/a.ml b/tests/test-dirs/issue1900.t/lib/a.ml
new file mode 100644
index 0000000000..e69de29bb2
diff --git a/tests/test-dirs/issue1900.t/lib/dune b/tests/test-dirs/issue1900.t/lib/dune
new file mode 100644
index 0000000000..67263ab7cf
--- /dev/null
+++ b/tests/test-dirs/issue1900.t/lib/dune
@@ -0,0 +1,2 @@
+(library
+ (name lib))
diff --git a/tests/test-dirs/issue1900.t/main.ml b/tests/test-dirs/issue1900.t/main.ml
new file mode 100644
index 0000000000..c6153208da
--- /dev/null
+++ b/tests/test-dirs/issue1900.t/main.ml
@@ -0,0 +1 @@
+prerr_endline A.x
diff --git a/tests/test-dirs/issue1900.t/run.t b/tests/test-dirs/issue1900.t/run.t
new file mode 100644
index 0000000000..ea0c643f77
--- /dev/null
+++ b/tests/test-dirs/issue1900.t/run.t
@@ -0,0 +1,78 @@
+  $ dune exec ./main.exe
+  test
+
+FIXME: There should be no error.
+  $ $MERLIN single errors -filename main.ml <main.ml | jq '.value'
+  [
+    {
+      "start": {
+        "line": 1,
+        "col": 14
+      },
+      "end": {
+        "line": 1,
+        "col": 17
+      },
+      "type": "typer",
+      "sub": [],
+      "valid": true,
+      "message": "Unbound value A.x"
+    }
+  ]
+
+FIXME: Dune should communicate the -open Dune__exe flag after the others.
+  $ $MERLIN single dump-configuration -filename main.ml <main.ml | \
+  > jq '.value.merlin.flags_applied'
+  [
+    {
+      "workdir": "$TESTCASE_ROOT",
+      "workval": [
+        "-open",
+        "Dune__exe"
+      ]
+    },
+    {
+      "workdir": "$TESTCASE_ROOT",
+      "workval": [
+        "-w",
+        "@1..3@5..28@30..39@43@46..47@49..57@61..62-40",
+        "-strict-sequence",
+        "-strict-formats",
+        "-short-paths",
+        "-keep-locs",
+        "-open",
+        "Lib",
+        "-g"
+      ]
+    }
+  ]
+
+Using a .merlin with the FLG flags in the correct order works:
+  $ cat >.merlin <<'EOF'
+  > B _build/default/.main.eobjs/byte
+  > B _build/default/lib/.lib.objs/byte
+  > FLG -open Lib
+  > FLG -open Dune__exe
+  > EOF
+
+  $ $MERLIN single dump-configuration -filename main.ml <main.ml | \
+  > jq '.value.merlin.flags_applied'
+  [
+    {
+      "workdir": "$TESTCASE_ROOT",
+      "workval": [
+        "-open",
+        "Lib"
+      ]
+    },
+    {
+      "workdir": "$TESTCASE_ROOT",
+      "workval": [
+        "-open",
+        "Dune__exe"
+      ]
+    }
+  ]
+
+  $ $MERLIN single errors -filename main.ml <main.ml | jq '.value'
+  []