diff --git a/sidecar/src/main/kotlin/dev/sanderling/sidecar/DriverBackend.kt b/sidecar/src/main/kotlin/dev/sanderling/sidecar/DriverBackend.kt
index 6a6c535..cbf729e 100644
--- a/sidecar/src/main/kotlin/dev/sanderling/sidecar/DriverBackend.kt
+++ b/sidecar/src/main/kotlin/dev/sanderling/sidecar/DriverBackend.kt
@@ -159,15 +159,15 @@ internal fun pollUntilStable(
     var streakStart = 0L
     while (System.currentTimeMillis() < deadline) {
         Thread.sleep(intervalMillis)
+        val readStart = System.currentTimeMillis()
         val current = try {
             snapshot()
         } catch (_: Exception) {
             null
         }
-        val now = System.currentTimeMillis()
         if (prior != null && current != null && prior == current) {
-            if (streakStart == 0L) streakStart = now
-            if (now - streakStart >= streakMillis) return
+            if (streakStart == 0L) streakStart = System.currentTimeMillis()
+            if (readStart - streakStart >= streakMillis) return
         } else {
             streakStart = 0L
         }
diff --git a/sidecar/src/test/kotlin/dev/sanderling/sidecar/StabilityPollTest.kt b/sidecar/src/test/kotlin/dev/sanderling/sidecar/StabilityPollTest.kt
index 29d8c79..b8008a6 100644
--- a/sidecar/src/test/kotlin/dev/sanderling/sidecar/StabilityPollTest.kt
+++ b/sidecar/src/test/kotlin/dev/sanderling/sidecar/StabilityPollTest.kt
@@ -20,12 +20,9 @@ class StabilityPollTest {
     }
 
     @Test fun slowSnapshotReadsDoNotEatTheStreak() {
-        // Every other test here uses an instant lambda and so passes whether or
-        // not a read is charged to the streak; this one is the difference.
-        // StubDriverBackend's waitForIdle polls a real `uiautomator dump`,
-        // which costs hundreds of milliseconds, so the slow read is the case it
-        // runs in.
-        val readMillis = 400L
+        // A hierarchy fetch costs about this on a physical device, which is the
+        // read pollUntilStable's contract works its numbers out against.
+        val readMillis = 500L
         val sampleStarts = mutableListOf<Long>()
         val sampleEnds = mutableListOf<Long>()
         val start = System.currentTimeMillis()
@@ -36,19 +33,18 @@ class StabilityPollTest {
             "stable"
         }
 
-        // What the poll actually watched: the last read began this long after
-        // the first one returned, and every sample in between matched.
-        val observedQuiet = sampleStarts.last() - sampleEnds.first()
+        assertTrue(
+            sampleStarts.size >= 3,
+            "a ${readMillis}ms read cannot clear the streak in one pair, starts=$sampleStarts",
+        )
+        val firstMatchingReadReturned = sampleEnds[1]
+        val observedQuiet = sampleStarts.last() - firstMatchingReadReturned
         assertTrue(
             observedQuiet >= MIN_STABLE_STREAK_MILLIS,
             "the poll returned having observed only ${observedQuiet}ms of " +
                 "quiet, not ${MIN_STABLE_STREAK_MILLIS}ms; " +
                 "starts=$sampleStarts ends=$sampleEnds",
         )
-        assertTrue(
-            sampleStarts.size >= 3,
-            "a ${readMillis}ms read cannot clear the streak in one pair, starts=$sampleStarts",
-        )
     }
 
     @Test fun streakResetsOnAnyChange() {