diff --git a/main/actions/src/main/scala/sbt/Tests.scala b/main/actions/src/main/scala/sbt/Tests.scala
index 486361565..22ae552cc 100644
--- a/main/actions/src/main/scala/sbt/Tests.scala
+++ b/main/actions/src/main/scala/sbt/Tests.scala
@@ -197,7 +197,11 @@ object Tests {
     val tasks = runnables.map { case (name, test) => toTask(loader, name, test, tags) }
     tasks.join.map(_.foldLeft(Map.empty[String, SuiteResult]) {
       case (sum, e) =>
-        sum ++ e
+        val merged = sum.toSeq ++ e.toSeq
+        val grouped = merged.groupBy(_._1)
+        grouped.mapValues(_.map(_._2).foldLeft(SuiteResult.Empty) {
+          case (resultSum, result) => resultSum + result
+        })
     })
   }
 
@@ -207,7 +211,14 @@ object Tests {
     taggedBase flatMap {
       case (name, (result, nested)) =>
         val nestedRunnables = createNestedRunnables(loader, fun, nested)
-        toTasks(loader, nestedRunnables, tags).map(_.updated(name, result))
+        toTasks(loader, nestedRunnables, tags).map { currentResultMap =>
+          val newResult =
+            currentResultMap.get(name) match {
+              case Some(currentResult) => currentResult + result
+              case None                => result
+            }
+          currentResultMap.updated(name, newResult)
+        }
     }
   }
 
diff --git a/testing/src/main/scala/sbt/TestReportListener.scala b/testing/src/main/scala/sbt/TestReportListener.scala
index 5a3e34072..d0d1d9562 100644
--- a/testing/src/main/scala/sbt/TestReportListener.scala
+++ b/testing/src/main/scala/sbt/TestReportListener.scala
@@ -28,9 +28,21 @@ trait TestsListener extends TestReportListener {
 
 /** Provides the overall `result` of a group of tests (a suite) and test counts for each result type. */
 final class SuiteResult(
-  val result: TestResult.Value,
-  val passedCount: Int, val failureCount: Int, val errorCount: Int,
-  val skippedCount: Int, val ignoredCount: Int, val canceledCount: Int, val pendingCount: Int)
+    val result: TestResult.Value,
+    val passedCount: Int, val failureCount: Int, val errorCount: Int,
+    val skippedCount: Int, val ignoredCount: Int, val canceledCount: Int, val pendingCount: Int) {
+  def +(other: SuiteResult): SuiteResult = {
+    val combinedTestResult =
+      (result, other.result) match {
+        case (TestResult.Passed, TestResult.Passed) => TestResult.Passed
+        case (_, TestResult.Error)                  => TestResult.Error
+        case (TestResult.Error, _)                  => TestResult.Error
+        case _                                      => TestResult.Failed
+      }
+    new SuiteResult(combinedTestResult, passedCount + other.passedCount, failureCount + other.failureCount, errorCount + other.errorCount, skippedCount + other.skippedCount,
+      ignoredCount + other.ignoredCount, canceledCount + other.canceledCount, pendingCount + other.pendingCount)
+  }
+}
 
 object SuiteResult {
   /** Computes the overall result and counts for a suite with individual test results in `events`. */