diff --git a/lib/Loop/NativeDriver.php b/lib/Loop/NativeDriver.php
index a64d2c5..c6b9936 100644
--- a/lib/Loop/NativeDriver.php
+++ b/lib/Loop/NativeDriver.php
@@ -230,7 +230,12 @@ final class NativeDriver extends Driver
             return;
         }
 
-        if ($timeout > 0) { // Otherwise sleep with usleep() if $timeout > 0.
+        if ($timeout < 0) { // Only signal watchers are enabled, so sleep indefinitely.
+            \usleep(\PHP_INT_MAX);
+            return;
+        }
+
+        if ($timeout > 0) { // Sleep until next timer expires.
             \usleep((int) ($timeout * self::MICROSEC_PER_SEC));
         }
     }
diff --git a/test/Loop/DriverTest.php b/test/Loop/DriverTest.php
index 38e3b87..a6abeb0 100644
--- a/test/Loop/DriverTest.php
+++ b/test/Loop/DriverTest.php
@@ -360,7 +360,7 @@ abstract class DriverTest extends TestCase
             \call_user_func_array([$loop, $type], $args);
 
             if ($type == "onSignal") {
-                $loop->defer(function (): void {
+                $loop->delay(1, function () {
                     \posix_kill(\getmypid(), \SIGUSR1);
                 });
             }
@@ -631,11 +631,11 @@ abstract class DriverTest extends TestCase
                     $loop->onSignal(\SIGUSR1, $fn = function ($watcherId, $signo, $i) use (&$fn, $loop, $sendSignal): void {
                         if ($i) {
                             $loop->onSignal(\SIGUSR1, $fn, --$i);
-                            $loop->defer($sendSignal);
+                            $loop->delay(1, $sendSignal);
                         }
                         $loop->cancel($watcherId);
                     }, $runs);
-                    $loop->defer($sendSignal);
+                    $loop->delay(1, $sendSignal);
                     $loop->run();
                 }
             };
@@ -783,7 +783,7 @@ abstract class DriverTest extends TestCase
             $loop->onSignal(SIGUSR1, $f(2));
             $loop->defer(function () use ($loop, $sig2): void {
                 $loop->enable($sig2);
-                $loop->defer(function () use ($loop): void {
+                $loop->delay(1, function () use ($loop) {
                     \posix_kill(\getmypid(), \SIGUSR1);
                     $loop->delay($msDelay = 10, function () use ($loop): void {
                         $loop->stop();