diff --git a/lib/ocaml/baseline/expected.json b/lib/ocaml/baseline/expected.json
index 01db65d7..90b61eb0 100644
--- a/lib/ocaml/baseline/expected.json
+++ b/lib/ocaml/baseline/expected.json
@@ -75,6 +75,7 @@
   "max_product3.ml": 300,
   "max_run.ml": 5,
   "mod_inverse.ml": 27,
+  "josephus.ml": 11,
   "json_pretty.ml": 24,
   "kadane.ml": 6,
   "lambda_calc.ml": 7,
diff --git a/lib/ocaml/baseline/josephus.ml b/lib/ocaml/baseline/josephus.ml
new file mode 100644
index 00000000..0d1970c0
--- /dev/null
+++ b/lib/ocaml/baseline/josephus.ml
@@ -0,0 +1,7 @@
+let rec josephus n k =
+  if n = 1 then 0
+  else (josephus (n - 1) k + k) mod n
+
+;;
+
+josephus 50 3 + 1
diff --git a/plans/ocaml-on-sx.md b/plans/ocaml-on-sx.md
index b4f6ac7e..bb56d80e 100644
--- a/plans/ocaml-on-sx.md
+++ b/plans/ocaml-on-sx.md
@@ -407,6 +407,11 @@ _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.
+- 2026-05-10 Phase 5.1 — josephus.ml baseline (Josephus problem,
+  n=50 k=3 → survivor at position 11, 1-indexed). Uses the classic
+  recursive formula: J(1, k) = 0; J(n, k) = (J(n-1, k) + k) mod n.
+  Returns 0-indexed survivor; we add 1 for human readability. Tests
+  recursion, mod, integer arithmetic. 136 baseline programs total.
 - 2026-05-10 Phase 5.1 — partition_count.ml baseline (number of
   integer partitions of 15 = 176). Classic DP: dp[0] = 1; for each
   k from 1..n, for each i from k..n, dp[i] += dp[i - k]. O(n²) time,