diff --git a/src/app/Rules/SignupExternalEmail.php b/src/app/Rules/SignupExternalEmail.php
--- a/src/app/Rules/SignupExternalEmail.php
+++ b/src/app/Rules/SignupExternalEmail.php
@@ -24,7 +24,7 @@
         // Don't allow multiple open registrations against the same email address
         if (($limit = \config('app.signup.email_limit')) > 0) {
             $signups = SignupCode::where('email', $email)
-                ->whereDate('expires_at', '>', \Carbon\Carbon::now());
+                ->where('expires_at', '>', \Carbon\Carbon::now());
 
             if ($signups->count() >= $limit) {
                 // @kanarip: this is deliberately an "email invalid" message
@@ -36,7 +36,7 @@
         // Don't allow multiple open registrations against the same source ip address
         if (($limit = \config('app.signup.ip_limit')) > 0) {
             $signups = SignupCode::where('ip_address', request()->ip())
-                ->whereDate('expires_at', '>', \Carbon\Carbon::now());
+                ->where('expires_at', '>', \Carbon\Carbon::now());
 
             if ($signups->count() >= $limit) {
                 // @kanarip: this is deliberately an "email invalid" message
diff --git a/src/database/migrations/2022_01_03_120000_signup_codes_indices.php b/src/database/migrations/2022_01_03_120000_signup_codes_indices.php
new file mode 100644
--- /dev/null
+++ b/src/database/migrations/2022_01_03_120000_signup_codes_indices.php
@@ -0,0 +1,43 @@
+<?php
+
+use Illuminate\Database\Migrations\Migration;
+use Illuminate\Database\Schema\Blueprint;
+use Illuminate\Support\Facades\Schema;
+
+// phpcs:ignore
+class SignupCodesIndices extends Migration
+{
+    /**
+     * Run the migrations.
+     *
+     * @return void
+     */
+    public function up()
+    {
+        Schema::table(
+            'signup_codes',
+            function (Blueprint $table) {
+                $table->index('email');
+                $table->index('ip_address');
+                $table->index('expires_at');
+            }
+        );
+    }
+
+    /**
+     * Reverse the migrations.
+     *
+     * @return void
+     */
+    public function down()
+    {
+        Schema::table(
+            'signup_codes',
+            function (Blueprint $table) {
+                $table->dropIndex('email');
+                $table->dropIndex('ip_address');
+                $table->dropIndex('expires_at');
+            }
+        );
+    }
+}