diff --git a/qualtran/surface_code/data_block.py b/qualtran/surface_code/data_block.py
index c0237613c..6d1eea99f 100644
--- a/qualtran/surface_code/data_block.py
+++ b/qualtran/surface_code/data_block.py
@@ -167,7 +167,7 @@ class CompactDataBlock(DataBlock):
     data_d: int
 
     def n_tiles(self, n_algo_qubits: int) -> int:
-        return math.ceil(1.5 * n_algo_qubits)
+        return math.ceil(1.5 * (n_algo_qubits + 2))
 
     @property
     def n_steps_to_consume_a_magic_state(self) -> int:
diff --git a/qualtran/surface_code/data_block_test.py b/qualtran/surface_code/data_block_test.py
index 86931572a..89f75208b 100644
--- a/qualtran/surface_code/data_block_test.py
+++ b/qualtran/surface_code/data_block_test.py
@@ -15,7 +15,7 @@
 
 import pytest
 
-from qualtran.surface_code import FastDataBlock, LogicalErrorModel, QECScheme
+from qualtran.surface_code import CompactDataBlock, FastDataBlock, LogicalErrorModel, QECScheme
 
 
 @pytest.mark.parametrize(
@@ -28,3 +28,10 @@ def test_fast_block(logical_qubits, logical_qubits_with_routing, data_error):
     assert FastDataBlock(3).data_error(
         n_algo_qubits=logical_qubits, n_cycles=3, logical_error_model=err_model
     ) == pytest.approx(data_error)
+
+@pytest.mark.parametrize(
+    ["n_algo_qubits", "n_tiles"],
+    [[2,6],[4,9],[100,153]]
+)
+def test_compact_block(n_algo_qubits, n_tiles):
+    assert CompactDataBlock(data_d=17).n_tiles(n_algo_qubits=n_algo_qubits) == n_tiles