diff --git a/lib/web_ui/dev/steps/run_tests_step.dart b/lib/web_ui/dev/steps/run_tests_step.dart
index 99a9cf7256189..ce47068050985 100644
--- a/lib/web_ui/dev/steps/run_tests_step.dart
+++ b/lib/web_ui/dev/steps/run_tests_step.dart
@@ -117,7 +117,7 @@ class RunTestsStep implements PipelineStep {
       );
     }
 
-    // Run all unit-tests as a single batch and with high concurrency.
+    // Run non-screenshot tests with high concurrency.
     if (unitTestFiles.isNotEmpty) {
       await _runTestBatch(
         testFiles: unitTestFiles,
@@ -130,11 +130,11 @@ class RunTestsStep implements PipelineStep {
       _checkExitCode('Unit tests');
     }
 
-    // Run screenshot tests one at a time. Otherwise, tests end up
-    // screenshotting each other.
-    for (final FilePath screenshotTestFilePath in screenshotTestFiles) {
+    // Run screenshot tests one at a time to prevent tests from screenshotting
+    // each other.
+    if (screenshotTestFiles.isNotEmpty) {
       await _runTestBatch(
-        testFiles: <FilePath>[screenshotTestFilePath],
+        testFiles: screenshotTestFiles,
         browserEnvironment: browserEnvironment,
         concurrency: 1,
         expectFailure: false,