diff --git a/poker/models.py b/poker/models.py
index e62df17..5ecda90 100644
--- a/poker/models.py
+++ b/poker/models.py
@@ -1,4 +1,4 @@
-from pydantic import BaseModel, Field
+from pydantic import BaseModel, validator
 
 from poker.constants import Suit, Value
 
@@ -9,8 +9,22 @@ class Card(BaseModel):
     suit: Suit
     value: Value
 
+    def __hash__(self) -> int:
+        """Hash function."""
+        return hash(f"{self.value} {self.suit}")
+
+
+HandType = tuple[Card, Card, Card, Card, Card]
+
 
 class Hand(BaseModel):
     """Hand domain model class."""
 
-    cards: list[Card] = Field(..., min_length=5, max_length=5)
+    cards: HandType
+
+    @validator("cards")
+    def validate_unique(cls, cards: HandType) -> HandType:
+        """Validate hand comprises unique cards."""
+        if len(cards) != len(set(cards)):
+            raise ValueError("Hand contains duplicate cards.")
+        return cards
diff --git a/tests/test_models.py b/tests/test_models.py
new file mode 100644
index 0000000..37e9c03
--- /dev/null
+++ b/tests/test_models.py
@@ -0,0 +1,28 @@
+import pytest
+from pydantic import ValidationError
+
+from poker.constants import Suit, Value
+from poker.models import Card, Hand
+
+
+def test_hand_should_contain_unique_cards() -> None:
+    with pytest.raises(ValidationError):
+        _ = Hand(
+            cards=(
+                Card(suit=Suit.CLUBS, value=Value.ACE),
+                Card(suit=Suit.CLUBS, value=Value.TWO),
+                Card(suit=Suit.CLUBS, value=Value.THREE),
+                Card(suit=Suit.CLUBS, value=Value.FOUR),
+                Card(suit=Suit.CLUBS, value=Value.FOUR),
+            )
+        )
+
+    _ = Hand(
+        cards=(
+            Card(suit=Suit.CLUBS, value=Value.ACE),
+            Card(suit=Suit.CLUBS, value=Value.TWO),
+            Card(suit=Suit.CLUBS, value=Value.THREE),
+            Card(suit=Suit.CLUBS, value=Value.FOUR),
+            Card(suit=Suit.CLUBS, value=Value.FIVE),
+        )
+    )