diff --git a/lib/ocaml/parser.sx b/lib/ocaml/parser.sx
index 2a5b0e4f..fc72ffdd 100644
--- a/lib/ocaml/parser.sx
+++ b/lib/ocaml/parser.sx
@@ -282,6 +282,56 @@
                     (list :pcons lhs (parse-pattern-cons))))
                 (else lhs)))))
         (set! parse-pattern (fn () (parse-pattern-cons)))
+
+        (define peek-tok-at
+          (fn (n)
+            (if (< (+ idx n) tok-len) (nth tokens (+ idx n)) nil)))
+
+        ;; Param consumption — matches ident, `_` (wildcard), or `()`
+        ;; (unit). Returns a fresh ident name or nil if no param at cursor.
+        (define wild-counter (list 0))
+        (define try-consume-param!
+          (fn ()
+            (cond
+              ((and (check-tok? "ident" nil)
+                    (= (ocaml-tok-value (peek-tok)) "_"))
+                (begin
+                  (advance-tok!)
+                  (set-nth! wild-counter 0 (+ (nth wild-counter 0) 1))
+                  (str "__wild_" (nth wild-counter 0))))
+              ((check-tok? "ident" nil)
+                (let ((nm (ocaml-tok-value (peek-tok))))
+                  (begin (advance-tok!) nm)))
+              ((and (at-op? "(") (= (ocaml-tok-value (peek-tok-at 1)) ")"))
+                (begin
+                  (advance-tok!) (advance-tok!)
+                  (set-nth! wild-counter 0 (+ (nth wild-counter 0) 1))
+                  (str "__unit_" (nth wild-counter 0))))
+              ((and (at-op? "(") (= (ocaml-tok-type (peek-tok-at 1)) "ident"))
+                ;; (x : T) — typed param. Skip the `: T` part.
+                (let ((nm (ocaml-tok-value (peek-tok-at 1))))
+                  (begin
+                    (advance-tok!) (advance-tok!)
+                    (when (at-op? ":")
+                      (begin
+                        ;; Skip until matching `)`.
+                        (let ((d 1))
+                          (begin
+                            (define skip
+                              (fn ()
+                                (cond
+                                  ((>= idx tok-len) nil)
+                                  ((at-op? "(")
+                                    (begin (set! d (+ d 1)) (advance-tok!) (skip)))
+                                  ((at-op? ")")
+                                    (cond
+                                      ((= d 1) nil)
+                                      (else (begin (set! d (- d 1)) (advance-tok!) (skip)))))
+                                  (else (begin (advance-tok!) (skip))))))
+                            (skip)))))
+                    (consume! "op" ")")
+                    nm)))
+              (else nil))))
         (define parse-expr (fn () nil))
         (define parse-expr-no-seq (fn () nil))
         (define parse-tuple (fn () nil))
@@ -492,14 +542,10 @@
               (begin
                 (define
                   collect-params
-                  (fn
-                    ()
-                    (when
-                      (check-tok? "ident" nil)
-                      (begin
-                        (append! params (ocaml-tok-value (peek-tok)))
-                        (advance-tok!)
-                        (collect-params)))))
+                  (fn ()
+                    (let ((nm (try-consume-param!)))
+                      (when (not (= nm nil))
+                        (begin (append! params nm) (collect-params))))))
                 (collect-params)
                 (when
                   (= (len params) 0)
@@ -522,14 +568,10 @@
                   (begin
                     (define
                       collect-params
-                      (fn
-                        ()
-                        (when
-                          (check-tok? "ident" nil)
-                          (begin
-                            (append! params (ocaml-tok-value (peek-tok)))
-                            (advance-tok!)
-                            (collect-params)))))
+                      (fn ()
+                        (let ((nm (try-consume-param!)))
+                          (when (not (= nm nil))
+                            (begin (append! params nm) (collect-params))))))
                     (collect-params)
                     (consume! "op" "=")
                     (let
@@ -806,11 +848,22 @@
                       (begin
                         (define collect-params
                           (fn ()
-                            (when (check-tok? "ident" nil)
-                              (begin
-                                (append! ps (ocaml-tok-value (peek-tok)))
-                                (advance-tok!)
-                                (collect-params)))))
+                            (cond
+                              ((check-tok? "ident" nil)
+                                (begin
+                                  (append! ps (ocaml-tok-value (peek-tok)))
+                                  (advance-tok!)
+                                  (collect-params)))
+                              ((and (at-op? "(")
+                                    (< (+ idx 1) tok-len)
+                                    (let ((t1 (nth tokens (+ idx 1))))
+                                      (and (= (ocaml-tok-type t1) "op")
+                                           (= (ocaml-tok-value t1) ")"))))
+                                (begin
+                                  (advance-tok!) (advance-tok!)
+                                  (append! ps (str "__unit_" idx))
+                                  (collect-params)))
+                              (else nil))))
                         (collect-params)
                         (consume! "op" "=")
                         (let ((expr-start (cur-pos)))
diff --git a/lib/ocaml/test.sh b/lib/ocaml/test.sh
index 5b87ac87..c204564f 100755
--- a/lib/ocaml/test.sh
+++ b/lib/ocaml/test.sh
@@ -702,9 +702,21 @@ cat > "$TMPFILE" << 'EPOCHS'
 (epoch 974)
 (eval "(ocaml-run \"Int.min 7 3\")")
 
+;; ── Unit / wildcard parameters ──────────────────────────────────
+(epoch 1000)
+(eval "(ocaml-run \"let f () = 42 in f ()\")")
+(epoch 1001)
+(eval "(ocaml-run \"(fun () -> 99) ()\")")
+(epoch 1002)
+(eval "(ocaml-run \"let f _ = 1 in f 5\")")
+(epoch 1003)
+(eval "(ocaml-run-program \"let f () = 7;; f ()\")")
+(epoch 1004)
+(eval "(ocaml-run-program \"let g _ x = x + 1;; g 99 41\")")
+
 EPOCHS
 
-OUTPUT=$(timeout 60 "$SX_SERVER" < "$TMPFILE" 2>/dev/null)
+OUTPUT=$(timeout 180 "$SX_SERVER" < "$TMPFILE" 2>/dev/null)
 
 check() {
   local epoch="$1" desc="$2" expected="$3"
@@ -1112,6 +1124,13 @@ check 972 "Int.abs -5"                   '5'
 check 973 "Int.max"                      '7'
 check 974 "Int.min"                      '3'
 
+# ── Unit / wildcard parameters ──────────────────────────────────
+check 1000 "let f () = 42 in f ()"        '42'
+check 1001 "(fun () -> 99) ()"            '99'
+check 1002 "let f _ = 1 in f 5"           '1'
+check 1003 "top-level let f () ="         '7'
+check 1004 "wildcard top-level"           '42'
+
 TOTAL=$((PASS + FAIL))
 if [ $FAIL -eq 0 ]; then
   echo "ok $PASS/$TOTAL OCaml-on-SX tests passed"
diff --git a/plans/ocaml-on-sx.md b/plans/ocaml-on-sx.md
index a7b756d1..9f051c29 100644
--- a/plans/ocaml-on-sx.md
+++ b/plans/ocaml-on-sx.md
@@ -343,6 +343,12 @@ the "mother tongue" closure: OCaml → SX → OCaml. This means:
 
 _Newest first._
 
+- 2026-05-08 Phase 1 — unit `()` and wildcard `_` parameters in `let f ()
+  = …` / `fun _ -> …` / `let f _ = …`. Parser helper `try-consume-param!`
+  now handles ident, wildcard `_` (renamed to `__wild_N`), unit `()`
+  (renamed to `__unit_N`), and typed `(x : T)` (signature skipped).
+  Same for top-level `parse-decl-let`. test.sh timeout extended from
+  60s to 180s for the growing suite. 283/283 (+5).
 - 2026-05-08 Phase 6 — extended stdlib slice (+13 tests, 278 total).
   Host primitives exposed via `_string_*`, `_char_*`, `_int_*`,
   `_string_of_*` underscore-prefixed builtins so the OCaml-side