diff --git a/moto/cognitoidp/models.py b/moto/cognitoidp/models.py
index e68a70b4e..cb1a5cf44 100644
--- a/moto/cognitoidp/models.py
+++ b/moto/cognitoidp/models.py
@@ -384,7 +384,7 @@ class CognitoIdpBackend(BaseBackend):
     def describe_user_pool(self, user_pool_id):
         user_pool = self.user_pools.get(user_pool_id)
         if not user_pool:
-            raise ResourceNotFoundError(user_pool_id)
+            raise ResourceNotFoundError(f"User pool {user_pool_id} does not exist.")
 
         return user_pool
 
diff --git a/tests/test_cognitoidp/test_cognitoidp.py b/tests/test_cognitoidp/test_cognitoidp.py
index a3e5be752..7cb8e8956 100644
--- a/tests/test_cognitoidp/test_cognitoidp.py
+++ b/tests/test_cognitoidp/test_cognitoidp.py
@@ -215,6 +215,19 @@ def test_describe_user_pool():
     result["UserPool"]["LambdaConfig"]["PreSignUp"].should.equal(value)
 
 
+@mock_cognitoidp
+def test_describe_user_pool_resource_not_found():
+    conn = boto3.client("cognito-idp", "us-east-1")
+
+    user_pool_id = "us-east-1_FooBar123"
+    with pytest.raises(ClientError) as exc:
+        conn.describe_user_pool(UserPoolId=user_pool_id)
+
+    err = exc.value.response["Error"]
+    err["Code"].should.equal("ResourceNotFoundException")
+    err["Message"].should.equal(f"User pool {user_pool_id} does not exist.")
+
+
 @mock_cognitoidp
 def test_update_user_pool():
     conn = boto3.client("cognito-idp", "us-east-1")