diff --git a/lib/ocaml/baseline/exception_user.ml b/lib/ocaml/baseline/exception_user.ml
new file mode 100644
index 00000000..1b00455a
--- /dev/null
+++ b/lib/ocaml/baseline/exception_user.ml
@@ -0,0 +1,16 @@
+exception Negative of int
+
+let safe_sqrt n =
+  if n < 0 then raise (Negative n)
+  else
+    let g = ref 1 in
+    while !g * !g < n do g := !g + 1 done;
+    !g
+
+let try_sqrt n =
+  try safe_sqrt n with
+  | Negative x -> -x
+
+;;
+
+try_sqrt 16 + try_sqrt 25 + try_sqrt (-7) + try_sqrt 100
diff --git a/lib/ocaml/baseline/expected.json b/lib/ocaml/baseline/expected.json
index 037e7084..bb5b75fe 100644
--- a/lib/ocaml/baseline/expected.json
+++ b/lib/ocaml/baseline/expected.json
@@ -15,6 +15,7 @@
   "coin_change.ml": 6,
   "csv.ml": 10,
   "exception_handle.ml": 4,
+  "exception_user.ml": 26,
   "expr_eval.ml": 16,
   "expr_simp.ml": 22,
   "factorial.ml": 3628800,
diff --git a/plans/ocaml-on-sx.md b/plans/ocaml-on-sx.md
index e185bb34..adcdbb15 100644
--- a/plans/ocaml-on-sx.md
+++ b/plans/ocaml-on-sx.md
@@ -407,6 +407,13 @@ _Newest first._
   binary search tree (`type 'a tree = Leaf | Node of 'a * 'a tree *
   'a tree`) with insert + in-order traversal. Tests parametric ADT,
   recursive match, List.append, List.fold_left.
+- 2026-05-09 Phase 5.1 — exception_user.ml baseline (user-defined
+  exception with int payload, 4+5+7+10 = 26). Defines `exception
+  Negative of int`, `safe_sqrt` raises it on negative input, and
+  `try_sqrt` catches with `try ... with | Negative x -> -x`. Tests
+  exception declaration, raise with carry-payload, try-with arm
+  matching the constructor and binding the payload. 56 baseline
+  programs total.
 - 2026-05-09 Phase 5.1 — flatten_tree.ml baseline (parametric ADT
   flatten, sum 1..7 = 28). Defines `type 'a tree = Leaf of 'a |
   Node of 'a tree list` then `flatten` recursively expands using