diff --git a/tests/test_monitor_graph_json.py b/tests/test_monitor_graph_json.py
index f9e958f..1b40ee9 100644
--- a/tests/test_monitor_graph_json.py
+++ b/tests/test_monitor_graph_json.py
@@ -484,6 +484,98 @@ class TestGraphJsonFinished:
         assert result["finished"] is True
 
 
+class TestTagStoreSerialisation:
+    """Test non-empty tag_store JSON serialization in PE state."""
+
+    def test_non_empty_tag_store_serialization(self):
+        """Test that tag_store with non-empty mapping serializes correctly."""
+        node = IRNode(
+            name="&add",
+            opcode=ArithOp.ADD,
+            pe=0,
+            iram_offset=0,
+            act_id=0,
+        )
+        ir_graph = IRGraph(nodes={"&add": node})
+
+        inst = Instruction(opcode=ArithOp.ADD, output=OutputStyle.INHERIT, has_const=False, dest_count=2, wide=False, fref=0)
+
+        # Create PESnapshot with non-empty tag_store: act_id 0 maps to frame 2, lane 1
+        pe_snap = PESnapshot(
+            pe_id=0,
+            iram={0: inst},
+            frames=(),
+            tag_store={0: (2, 1)},  # act_id=0 -> (frame_id=2, lane=1)
+            presence=(),
+            port_store=(),
+            match_data=(),
+            free_frames=(),
+            lane_count=4,
+            input_queue=(),
+            output_log=(),
+        )
+        snapshot = StateSnapshot(
+            sim_time=0.0,
+            next_time=1.0,
+            pes={0: pe_snap},
+            sms={},
+        )
+
+        result = graph_loaded_json(ir_graph, snapshot)
+        pe_state = result["state"]["pes"]["0"]
+
+        # Verify tag_store is correctly serialized
+        assert "tag_store" in pe_state
+        assert "0" in pe_state["tag_store"]  # act_id 0 should be a string key "0"
+        assert pe_state["tag_store"]["0"]["frame_id"] == 2
+        assert pe_state["tag_store"]["0"]["lane"] == 1
+        assert pe_state["lane_count"] == 4
+
+    def test_multiple_entries_tag_store_serialization(self):
+        """Test tag_store with multiple act_id entries serializes correctly."""
+        ir_graph = IRGraph()
+
+        inst = Instruction(opcode=ArithOp.ADD, output=OutputStyle.INHERIT, has_const=False, dest_count=2, wide=False, fref=0)
+
+        # Create PESnapshot with multiple tag_store entries
+        pe_snap = PESnapshot(
+            pe_id=0,
+            iram={0: inst},
+            frames=(),
+            tag_store={
+                0: (2, 1),
+                1: (3, 0),
+                5: (7, 2),
+            },
+            presence=(),
+            port_store=(),
+            match_data=(),
+            free_frames=(),
+            lane_count=4,
+            input_queue=(),
+            output_log=(),
+        )
+        snapshot = StateSnapshot(
+            sim_time=0.0,
+            next_time=1.0,
+            pes={0: pe_snap},
+            sms={},
+        )
+
+        result = graph_loaded_json(ir_graph, snapshot)
+        pe_state = result["state"]["pes"]["0"]
+
+        # Verify all entries are correctly serialized
+        assert "tag_store" in pe_state
+        assert pe_state["tag_store"]["0"]["frame_id"] == 2
+        assert pe_state["tag_store"]["0"]["lane"] == 1
+        assert pe_state["tag_store"]["1"]["frame_id"] == 3
+        assert pe_state["tag_store"]["1"]["lane"] == 0
+        assert pe_state["tag_store"]["5"]["frame_id"] == 7
+        assert pe_state["tag_store"]["5"]["lane"] == 2
+        assert pe_state["lane_count"] == 4
+
+
 class TestAC72_NewEventTypesSerialization:
     """AC7.2: Verify new frame-based event types serialize correctly to JSON."""