diff --git a/lib/minikanren/clpfd.sx b/lib/minikanren/clpfd.sx
index e356e60a..fedc87c7 100644
--- a/lib/minikanren/clpfd.sx
+++ b/lib/minikanren/clpfd.sx
@@ -459,3 +459,28 @@
     (cond
       ((empty? vars) succeed)
       (:else (mk-conj (fd-label-one (first vars)) (fd-label (rest vars)))))))
+
+;; --- fd-distinct (pairwise distinct via fd-neq) ---
+
+(define
+  fd-distinct-from-head
+  (fn
+    (x others)
+    (cond
+      ((empty? others) succeed)
+      (:else
+        (mk-conj
+          (fd-neq x (first others))
+          (fd-distinct-from-head x (rest others)))))))
+
+(define
+  fd-distinct
+  (fn
+    (vars)
+    (cond
+      ((empty? vars) succeed)
+      ((empty? (rest vars)) succeed)
+      (:else
+        (mk-conj
+          (fd-distinct-from-head (first vars) (rest vars))
+          (fd-distinct (rest vars)))))))
diff --git a/lib/minikanren/tests/clpfd-distinct.sx b/lib/minikanren/tests/clpfd-distinct.sx
new file mode 100644
index 00000000..1c2d7d11
--- /dev/null
+++ b/lib/minikanren/tests/clpfd-distinct.sx
@@ -0,0 +1,52 @@
+;; lib/minikanren/tests/clpfd-distinct.sx — fd-distinct (alldifferent).
+
+(mk-test
+  "fd-distinct-empty"
+  (run* q (fd-distinct (list)))
+  (list (make-symbol "_.0")))
+
+(mk-test
+  "fd-distinct-singleton"
+  (run* q (fd-distinct (list 5)))
+  (list (make-symbol "_.0")))
+
+(mk-test
+  "fd-distinct-pair-distinct"
+  (run* q (fd-distinct (list 1 2)))
+  (list (make-symbol "_.0")))
+
+(mk-test
+  "fd-distinct-pair-equal-fails"
+  (run* q (fd-distinct (list 5 5)))
+  (list))
+
+(mk-test
+  "fd-distinct-3-perms-of-3"
+  (let
+    ((res (run* q (fresh (a b c) (fd-in a (list 1 2 3)) (fd-in b (list 1 2 3)) (fd-in c (list 1 2 3)) (fd-distinct (list a b c)) (fd-label (list a b c)) (== q (list a b c))))))
+    (= (len res) 6))
+  true)
+
+(mk-test
+  "fd-distinct-4-perms-of-4-count"
+  (let
+    ((res (run* q (fresh (a b c d) (fd-in a (list 1 2 3 4)) (fd-in b (list 1 2 3 4)) (fd-in c (list 1 2 3 4)) (fd-in d (list 1 2 3 4)) (fd-distinct (list a b c d)) (fd-label (list a b c d)) (== q (list a b c d))))))
+    (= (len res) 24))
+  true)
+
+(mk-test
+  "fd-distinct-pigeonhole-fails"
+  (run*
+    q
+    (fresh
+      (a b c d)
+      (fd-in a (list 1 2 3))
+      (fd-in b (list 1 2 3))
+      (fd-in c (list 1 2 3))
+      (fd-in d (list 1 2 3))
+      (fd-distinct (list a b c d))
+      (fd-label (list a b c d))
+      (== q (list a b c d))))
+  (list))
+
+(mk-tests-run!)