diff --git a/tests/test-dirs/config/issue1388.t b/tests/test-dirs/config/issue1388.t
new file mode 100644
index 0000000000..4987bdec99
--- /dev/null
+++ b/tests/test-dirs/config/issue1388.t
@@ -0,0 +1,32 @@
+  $ cat >.merlin <<EOF
+  > STDLIB /my/std
+  > FLG -I +../cerberus/flags
+  > S +../cerberus/source
+  > B +../cerberus/build
+  > EOF
+
+FIXME include_dir should also replace the `+` by the lib path
+  $ echo "" | $MERLIN single dump-configuration -filename test.ml | \
+  > grep -A2 'include_dirs\|source_path\|build_path'
+        "include_dirs": [
+          "$TESTCASE_ROOT/+../cerberus/flags"
+        ],
+  --
+        "build_path": [
+          "/my/cerberus/build"
+        ],
+        "source_path": [
+          "/my/cerberus/source"
+        ],
+
+  $ echo "" | $MERLIN single dump -what paths -filename test.ml 
+  {
+    "class": "return",
+    "value": [
+      "$TESTCASE_ROOT",
+      "$TESTCASE_ROOT/+../cerberus/flags",
+      "/my/cerberus/build",
+      "lib/ocaml"
+    ],
+    "notifications": []
+  }