diff --git a/src/Collections/TUniqueValues.php b/src/Collections/TUniqueValues.php
new file mode 100644
index 0000000..e4c4dbd
--- /dev/null
+++ b/src/Collections/TUniqueValues.php
@@ -0,0 +1,36 @@
+<?php
+
+namespace jrosset\Collections;
+
+/**
+ * Implementation for unique collection
+ *
+ * @psalm-template     TKey of array-key
+ * @template-covariant TValue
+ * @template-extends ImmutableCollection<TKey, TValue>
+ */
+trait TUniqueValues {
+    /**
+     * @inheritDoc
+     */
+    protected function _set ($key, $value): self {
+        if ($this->contains($value)) {
+            return $this;
+        }
+
+        $this->elements[$this->_normalizeKey($key)] = $value;
+        return $this;
+    }
+    /**
+     * @inheritDoc
+     */
+    protected function _add (...$values): self {
+        foreach ($values as $value) {
+            if ($this->contains($value)) {
+                continue;
+            }
+            $this->elements[] = $value;
+        }
+        return $this;
+    }
+}
\ No newline at end of file
diff --git a/src/Collections/UniqueCollection.php b/src/Collections/UniqueCollection.php
new file mode 100644
index 0000000..905f7b4
--- /dev/null
+++ b/src/Collections/UniqueCollection.php
@@ -0,0 +1,15 @@
+<?php
+
+namespace jrosset\Collections;
+
+/**
+ * A collection with unique values
+ *
+ * @psalm-template     TKey of array-key
+ * @template-covariant TValue
+ * @template-extends Collection<TKey, TValue>
+ * @template-extends TUniqueValues<TKey, TValue>
+ */
+class UniqueCollection extends Collection {
+    use TUniqueValues;
+}
\ No newline at end of file
diff --git a/src/Collections/UniqueImmutableCollection.php b/src/Collections/UniqueImmutableCollection.php
new file mode 100644
index 0000000..6ce640d
--- /dev/null
+++ b/src/Collections/UniqueImmutableCollection.php
@@ -0,0 +1,15 @@
+<?php
+
+namespace jrosset\Collections;
+
+/**
+ * An immutable collection with unique values
+ *
+ * @psalm-template     TKey of array-key
+ * @template-covariant TValue
+ * @template-extends ImmutableCollection<TKey, TValue>
+ * @template-extends TUniqueValues<TKey, TValue>
+ */
+class UniqueImmutableCollection extends ImmutableCollection {
+    use TUniqueValues;
+}
\ No newline at end of file