diff --git a/src/main/java/com/google/devtools/build/lib/analysis/RuleConfiguredTargetBuilder.java b/src/main/java/com/google/devtools/build/lib/analysis/RuleConfiguredTargetBuilder.java
index 8a6a9728894f70..9a9fd613ba378a 100644
--- a/src/main/java/com/google/devtools/build/lib/analysis/RuleConfiguredTargetBuilder.java
+++ b/src/main/java/com/google/devtools/build/lib/analysis/RuleConfiguredTargetBuilder.java
@@ -209,7 +209,7 @@ public ConfiguredTarget build() throws ActionConflictException, InterruptedExcep
 
     if (ruleContext.getRule().hasAnalysisTestTransition()) {
       NestedSet<Label> labels = transitiveLabels();
-      int depCount = labels.toList().size();
+      int depCount = labels.memoizedFlattenAndGetSize();
       if (depCount > ruleContext.getConfiguration().analysisTestingDepsLimit()) {
         ruleContext.ruleError(
             String.format(