diff --git a/.idea/four-letter-blocks.iml b/.idea/four-letter-blocks.iml
index ac6d40f..e9c1ecd 100644
--- a/.idea/four-letter-blocks.iml
+++ b/.idea/four-letter-blocks.iml
@@ -6,7 +6,7 @@
       <excludeFolder url="file://$MODULE_DIR$/build" />
       <excludeFolder url="file://$MODULE_DIR$/dist" />
     </content>
-    <orderEntry type="jdk" jdkName="Python 3.10 (four-letter-blocks-Mirmoh7N)" jdkType="Python SDK" />
+    <orderEntry type="jdk" jdkName="Python 3.12 (four-letter-blocks-Mirmoh7N)" jdkType="Python SDK" />
     <orderEntry type="sourceFolder" forTests="false" />
   </component>
   <component name="TestRunnerService">
diff --git a/.idea/misc.xml b/.idea/misc.xml
index c807d2f..fe25f72 100644
--- a/.idea/misc.xml
+++ b/.idea/misc.xml
@@ -3,5 +3,5 @@
   <component name="Black">
     <option name="sdkName" value="Python 3.10 (four-letter-blocks-Mirmoh7N)" />
   </component>
-  <component name="ProjectRootManager" version="2" project-jdk-name="Python 3.10 (four-letter-blocks-Mirmoh7N)" project-jdk-type="Python SDK" />
+  <component name="ProjectRootManager" version="2" languageLevel="JDK_22" project-jdk-name="Python 3.10 (four-letter-blocks-Mirmoh7N)" project-jdk-type="Python SDK" />
 </project>
\ No newline at end of file
diff --git a/four_letter_blocks/block_packer.py b/four_letter_blocks/block_packer.py
index 1499379..a430825 100644
--- a/four_letter_blocks/block_packer.py
+++ b/four_letter_blocks/block_packer.py
@@ -74,7 +74,7 @@ def rotated_positions(self):
                 rotated_positions[rotated_shape].append((x, y))
         return rotated_positions
 
-    def find_slots(self) -> dict[str, np.ndarray]:
+    def find_slots(self, is_rotation_allowed=False) -> dict[str, np.ndarray]:
         if self.state is None:
             raise RuntimeError('Cannot find slots with invalid state.')
 
@@ -100,7 +100,14 @@ def find_slots(self) -> dict[str, np.ndarray]:
             has_even = np.logical_not(np.any(is_uneven, axis=(2, 3)))
 
             usable_slots = np.logical_and(open_slots, has_even)
-            slots[shape] = usable_slots
+            if not is_rotation_allowed or len(shape) == 1:
+                slots[shape] = usable_slots
+            else:
+                reported_shape = shape[0]
+                already_usable = slots.get(reported_shape)
+                if already_usable is not None:
+                    usable_slots = np.logical_or(usable_slots, already_usable)
+                slots[reported_shape] = usable_slots
         return slots
 
     def display(self, state: np.ndarray | None = None) -> str:
@@ -355,6 +362,13 @@ def shape_coordinates() -> typing.Dict[str, typing.List[np.ndarray]]:
 
 @cache
 def build_masks(width: int, height: int) -> dict[str, np.ndarray]:
+    """ Build the masks for each shape in each position.
+
+    :return: {shape_name: mask_array}, where mask_array is a four-dimensional
+        array of occupied spaces with index (start_row, start_col, row, col). In
+        other words, if the shape starts at (start_row, start_col), is
+        (row, col) filled?
+    """
     all_coordinates = shape_coordinates()
     all_masks = {}
     for shape, coordinate_list in all_coordinates.items():
diff --git a/tests/test_block_packer.py b/tests/test_block_packer.py
index 7f2e2d5..39ac93b 100644
--- a/tests/test_block_packer.py
+++ b/tests/test_block_packer.py
@@ -358,6 +358,7 @@ def test_fill_fail():
     assert not is_filled
 
 
+# noinspection DuplicatedCode
 def test_find_slots():
     packer = BlockPacker(start_text=dedent("""\
         #..#.
@@ -378,6 +379,45 @@ def test_find_slots():
     assert np.array_equal(o_slots, expected_o_slots)
 
 
+# noinspection DuplicatedCode
+def test_find_slots_rotation_allowed():
+    packer = BlockPacker(start_text=dedent("""\
+        #..#.
+        .....
+        ..#..
+        .....
+        .#..#"""))
+    # Not at (1, 3) or (2, 0), because they cut off something.
+    expected_s0_slots = np.array(object=[[1, 0, 0, 0, 0],
+                                         [0, 0, 0, 0, 0],
+                                         [0, 0, 0, 0, 0],
+                                         [0, 0, 1, 0, 0],
+                                         [0, 0, 0, 0, 0]],
+                                 dtype=bool)
+    expected_s1_slots = np.array(object=[[0, 0, 1, 0, 0],
+                                         [0, 0, 0, 0, 0],
+                                         [0, 1, 0, 0, 0],
+                                         [0, 0, 0, 0, 0],
+                                         [0, 0, 0, 0, 0]],
+                                 dtype=bool)
+    expected_s_slots = np.array(object=[[1, 0, 1, 0, 0],
+                                        [0, 0, 0, 0, 0],
+                                        [0, 1, 0, 0, 0],
+                                        [0, 0, 1, 0, 0],
+                                        [0, 0, 0, 0, 0]],
+                                dtype=bool)
+
+    is_rotation_allowed = False
+    s0_slots = packer.find_slots(is_rotation_allowed)['S0']
+    s1_slots = packer.find_slots()['S1']
+    is_rotation_allowed = True
+    s_slots = packer.find_slots(is_rotation_allowed)['S']
+
+    assert np.array_equal(s0_slots, expected_s0_slots)
+    assert np.array_equal(s1_slots, expected_s1_slots)
+    assert np.array_equal(s_slots, expected_s_slots)
+
+
 def test_find_slots_after_fail():
     packer = BlockPacker(start_text=dedent("""\
         #..#.