diff --git a/setup.php b/setup.php
index 1519b4a..04de2bd 100644
--- a/setup.php
+++ b/setup.php
@@ -8,7 +8,7 @@ if ($conn->connect_error) {
     die("Connection failed: " . $conn->connect_error);
 }
 
-$sql = "CREATE TABLE tracker ( ts TIMESTAMP PRIMARY KEY DEFAULT CURRENT_TIMESTAMP, lat DOUBLE, lon DOUBLE );";
+$sql = "CREATE TABLE tracker ( ts TIMESTAMP DEFAULT CURRENT_TIMESTAMP, device VARCHAR(38), lat DOUBLE, lon DOUBLE, PRIMARY KEY(ts, device) );";
 
 if (!mysqli_query($conn, $sql)) {
     die('Error: ' . mysqli_error($conn));