diff --git a/tests/csapi/txnid_test.go b/tests/csapi/txnid_test.go
new file mode 100644
index 00000000..5855d4ff
--- /dev/null
+++ b/tests/csapi/txnid_test.go
@@ -0,0 +1,41 @@
+package csapi_tests
+
+import (
+	"github.com/matrix-org/complement/internal/b"
+	"github.com/matrix-org/complement/internal/client"
+	"github.com/matrix-org/complement/runtime"
+	"github.com/tidwall/gjson"
+	"testing"
+)
+
+// TestTxnInEvent checks that the transaction ID is present when getting the event from the /rooms/{roomID}/event/{eventID} endpoint.
+func TestTxnInEvent(t *testing.T) {
+	// Dendrite implementation is broken
+	// See https://github.com/matrix-org/dendrite/issues/3000
+	runtime.SkipIf(t, runtime.Dendrite)
+
+	deployment := Deploy(t, b.BlueprintCleanHS)
+	defer deployment.Destroy(t)
+
+	c := deployment.RegisterUser(t, "hs1", "alice", "password", false)
+
+	// Create a room where we can send events.
+	roomID := c.CreateRoom(t, map[string]interface{}{})
+
+	// Let's send an event, and wait for it to appear in the timeline.
+	eventID := c.SendEventSynced(t, roomID, b.Event{
+		Type: "m.room.message",
+		Content: map[string]interface{}{
+			"msgtype": "m.text",
+			"body":    "first",
+		},
+	})
+
+	// The transaction ID should be present on the GET /rooms/{roomID}/event/{eventID} response.
+	res := c.MustDoFunc(t, "GET", []string{"_matrix", "client", "v3", "rooms", roomID, "event", eventID})
+	body := client.ParseJSON(t, res)
+	result := gjson.ParseBytes(body)
+	if !result.Get("unsigned.transaction_id").Exists() {
+		t.Fatalf("Event did not have a 'transaction_id' on the GET /rooms/%s/event/%s response", roomID, eventID)
+	}
+}