diff --git a/database/migrations/2021_02_01_000000_add_unique_key_to_poly_lines.php b/database/migrations/2021_02_01_000000_add_unique_key_to_poly_lines.php
new file mode 100644
index 000000000..778acab25
--- /dev/null
+++ b/database/migrations/2021_02_01_000000_add_unique_key_to_poly_lines.php
@@ -0,0 +1,21 @@
+<?php
+
+use Illuminate\Database\Migrations\Migration;
+use Illuminate\Database\Schema\Blueprint;
+use Illuminate\Support\Facades\Schema;
+
+class AddUniqueKeyToPolyLines extends Migration
+{
+    public function up(): void {
+        Schema::table('poly_lines', function(Blueprint $table) {
+            $table->unique(['hash']);
+        });
+    }
+
+
+    public function down(): void {
+        Schema::table('poly_lines', function(Blueprint $table) {
+            $table->dropUnique(['hash']);
+        });
+    }
+}