diff --git a/BuildMonitor.Test/BuildPriorityTests.cs b/BuildMonitor.Test/BuildPriorityTests.cs
new file mode 100644
index 0000000..b91a291
--- /dev/null
+++ b/BuildMonitor.Test/BuildPriorityTests.cs
@@ -0,0 +1,102 @@
+// Copyright (c) 2023-2026 ktsu-dev contributors
+
+namespace ktsu.BuildMonitor.Test;
+
+using ktsu.Semantics.Strings;
+
+using Microsoft.VisualStudio.TestTools.UnitTesting;
+
+/// <summary>
+/// Covers how a build's polling priority reads its runs. It used to read only the most recently started
+/// run across every branch, so a long run on main still going after a later PR run had finished dropped
+/// the build to Low, and main then failing never reached the recent-failure tier
+/// (ktsu-dev/BuildMonitor#392).
+/// </summary>
+[TestClass]
+public sealed class BuildPriorityTests
+{
+	private static readonly DateTimeOffset T0 = new(2026, 11, 3, 6, 0, 0, TimeSpan.Zero);
+
+	[TestCleanup]
+	public void Cleanup() => Clock.Reset();
+
+	private static Run AddRun(Build build, string id, string branch, DateTimeOffset started, RunStatus status, DateTimeOffset lastUpdated)
+	{
+		Run run = build.CreateRun(id.As<RunName>());
+		run.Branch = branch.As<BranchName>();
+		run.Started = started;
+		run.Status = status;
+		run.LastUpdated = lastUpdated;
+		build.Runs[run.Id] = run;
+		build.UpdateFromRun(run);
+		return run;
+	}
+
+	[TestMethod]
+	public void ARunStillGoingOnAnotherBranchKeepsTheBuildHigh()
+	{
+		// Arrange
+		Clock.UtcNowOverride = () => T0.AddMinutes(13);
+		Build build = new();
+		AddRun(build, "1", "main", T0, RunStatus.Running, T0.AddMinutes(12));
+		AddRun(build, "2", "feature", T0.AddMinutes(10), RunStatus.Success, T0.AddMinutes(12));
+
+		// Act
+		RequestPriority priority = new BuildSync { Build = build }.Priority;
+
+		// Assert
+		Assert.AreEqual(RequestPriority.High, priority, "main is still running, so the build should be polled at the running rate");
+	}
+
+	[TestMethod]
+	public void AFailureOnAnotherBranchIsARecentFailure()
+	{
+		// Arrange
+		Clock.UtcNowOverride = () => T0.AddMinutes(21);
+		Build build = new();
+		Run main = AddRun(build, "1", "main", T0, RunStatus.Running, T0.AddMinutes(12));
+		AddRun(build, "2", "feature", T0.AddMinutes(10), RunStatus.Success, T0.AddMinutes(12));
+
+		// Act
+		main.Status = RunStatus.Failure;
+		main.LastUpdated = T0.AddMinutes(20);
+		build.UpdateFromRun(main);
+		RequestPriority priority = new BuildSync { Build = build }.Priority;
+
+		// Assert
+		Assert.AreEqual(RequestPriority.Medium, priority, "main's newest run failed a minute ago");
+	}
+
+	[TestMethod]
+	public void AnOlderFailureSupersededOnItsBranchIsNotRecent()
+	{
+		// Arrange
+		Clock.UtcNowOverride = () => T0.AddMinutes(30);
+		Build build = new();
+		AddRun(build, "1", "main", T0, RunStatus.Failure, T0.AddMinutes(5));
+		AddRun(build, "2", "main", T0.AddMinutes(10), RunStatus.Success, T0.AddMinutes(15));
+		AddRun(build, "3", "feature", T0.AddMinutes(20), RunStatus.Success, T0.AddMinutes(25));
+
+		// Act
+		RequestPriority priority = new BuildSync { Build = build }.Priority;
+
+		// Assert
+		Assert.AreEqual(RequestPriority.Low, priority, "main's failure was fixed by a later run on main");
+	}
+
+	[TestMethod]
+	public void AFailureOverAnHourOldIsLow()
+	{
+		// Arrange
+		Clock.UtcNowOverride = () => T0.AddHours(3);
+		Build build = new();
+		AddRun(build, "1", "main", T0, RunStatus.Failure, T0.AddMinutes(20));
+		AddRun(build, "2", "feature", T0.AddMinutes(10), RunStatus.Success, T0.AddMinutes(12));
+
+		// Act
+		RequestPriority priority = new BuildSync { Build = build }.Priority;
+
+		// Assert
+		Assert.AreEqual(RequestPriority.Low, priority);
+	}
+}
diff --git a/BuildMonitor/Build.cs b/BuildMonitor/Build.cs
index 4908cd0..bbba8c9 100644
--- a/BuildMonitor/Build.cs
+++ b/BuildMonitor/Build.cs
@@ -24,6 +24,31 @@ internal sealed class Build
 	public RunStatus LastStatus { get; set; }
 	internal bool IsOngoing => !Runs.IsEmpty && LastStatus is RunStatus.Pending or RunStatus.Running;
 
+	/// <summary>
+	/// Gets a value indicating whether any of the build's runs, on any branch, is still pending or running.
+	/// <see cref="IsOngoing"/> reads only the most recently started run, so an earlier run on another
+	/// branch that is still going was missed once a later one finished (ktsu-dev/BuildMonitor#392).
+	/// </summary>
+	internal bool HasOngoingRun => IsOngoing || Runs.Values.Any(run => run.IsOngoing);
+
+	/// <summary>
+	/// Returns whether the newest run on any branch failed and was last updated after <paramref name="since"/>.
+	/// </summary>
+	/// <param name="since">The earliest update time that counts as recent.</param>
+	/// <returns><see langword="true"/> if some branch's newest run is a recent failure.</returns>
+	internal bool HasRecentBranchFailure(DateTimeOffset since)
+	{
+		if (LastStatus == RunStatus.Failure && LastUpdated > since)
+		{
+			return true;
+		}
+
+		return Runs.Values
+			.GroupBy(run => run.Branch)
+			.Select(branch => branch.MaxBy(run => run.Started)!)
+			.Any(newest => newest.Status == RunStatus.Failure && newest.LastUpdated > since);
+	}
+
 	/// <summary>
 	/// Calculates the estimated duration for this build using sophisticated statistical methods.
 	/// Uses all successful runs across all branches.
diff --git a/BuildMonitor/BuildSync.cs b/BuildMonitor/BuildSync.cs
index ffebdc5..3ff3052 100644
--- a/BuildMonitor/BuildSync.cs
+++ b/BuildMonitor/BuildSync.cs
@@ -54,15 +54,14 @@ internal RequestPriority Priority
 	{
 		get
 		{
-			// Running builds are highest priority
-			if (Build.IsOngoing)
+			// Running builds are highest priority, whichever branch the running run is on
+			if (Build.HasOngoingRun)
 			{
 				return RequestPriority.High;
 			}
 
-			// Recent failures are medium priority (within last hour)
-			if (Build.LastStatus == RunStatus.Failure &&
-				Build.LastUpdated > Clock.UtcNow.AddHours(-1))
+			// Recent failures are medium priority (within last hour), on any branch
+			if (Build.HasRecentBranchFailure(Clock.UtcNow.AddHours(-1)))
 			{
 				return RequestPriority.Medium;
 			}