diff --git a/src/main/java/com/google/devtools/build/lib/packages/Package.java b/src/main/java/com/google/devtools/build/lib/packages/Package.java
index 473153c00c1544..c33f4331cef431 100644
--- a/src/main/java/com/google/devtools/build/lib/packages/Package.java
+++ b/src/main/java/com/google/devtools/build/lib/packages/Package.java
@@ -2092,14 +2092,10 @@ public Package finishBuild() {
         return pkg;
       }
 
-      // Freeze targets and distributions.
+      // Freeze rules, compacting their attributes' representations.
       for (Rule rule : getRules()) {
         rule.freeze();
       }
-      ruleLabels = null;
-      rulesCreatedInMacros = null;
-      outputFilePrefixes = null;
-      targets = Maps.unmodifiableBiMap(targets);
 
       // Now all targets have been loaded, so we validate the group's member environments.
       for (EnvironmentGroup envGroup : ImmutableSet.copyOf(environmentGroups.values())) {
diff --git a/src/main/java/com/google/devtools/build/lib/packages/TargetRegistrationEnvironment.java b/src/main/java/com/google/devtools/build/lib/packages/TargetRegistrationEnvironment.java
index 2bb0951ef69e33..e7b0e4d1021ee4 100644
--- a/src/main/java/com/google/devtools/build/lib/packages/TargetRegistrationEnvironment.java
+++ b/src/main/java/com/google/devtools/build/lib/packages/TargetRegistrationEnvironment.java
@@ -167,7 +167,7 @@ private enum NameConflictCheckingPolicy {
    * <p>This field is null if name conflict checking is disabled. It is also null after the package
    * is built. The content of the map is manipulated only in {@link #checkRuleAndOutputs}.
    */
-  @Nullable protected Map<String, OutputFile> outputFilePrefixes = new HashMap<>();
+  @Nullable private Map<String, OutputFile> outputFilePrefixes = new HashMap<>();
 
   protected TargetRegistrationEnvironment(RepositoryMapping mainRepositoryMapping) {
     super(mainRepositoryMapping);