diff --git a/ext/standard/tests/hrtime/hrtime.phpt b/ext/standard/tests/hrtime/hrtime.phpt
index 614056c7d336..f221dda076c0 100644
--- a/ext/standard/tests/hrtime/hrtime.phpt
+++ b/ext/standard/tests/hrtime/hrtime.phpt
@@ -5,10 +5,15 @@ This test frequently fails in CI
 --FILE--
 <?php
 
+/* Busy-wait for a fixed amount of wall clock time instead of for a fixed
+ * number of iterations. The relative uncertainty checked below is dominated
+ * by scheduling jitter between the microtime() and hrtime() calls, so it is
+ * only meaningful once the measured interval is long enough to dwarf it. */
 $m0 = microtime(true);
 $h0 = hrtime(true);
-for ($i = 0; $i < 1024*1024; $i++);
-$h1 = hrtime(true);
+do {
+    $h1 = hrtime(true);
+} while ($h1 - $h0 < 100000000); /* 100ms */
 $m1 = microtime(true);
 
 $d0 = ($m1 - $m0)*1000000000.0;