1 files changed, 6 insertions, 5 deletions
diff --git a/src/main/java/com/google/devtools/build/lib/query2/engine/LetExpression.java b/src/main/java/com/google/devtools/build/lib/query2/engine/LetExpression.java
index a7c3abeb62..05021e6f8a 100644
--- a/src/main/java/com/google/devtools/build/lib/query2/engine/LetExpression.java
+++ b/src/main/java/com/google/devtools/build/lib/query2/engine/LetExpression.java
@@ -15,8 +15,8 @@ package com.google.devtools.build.lib.query2.engine;
 
 import com.google.common.base.Function;
 import com.google.devtools.build.lib.query2.engine.QueryEnvironment.QueryTaskFuture;
+import com.google.devtools.build.lib.query2.engine.QueryEnvironment.ThreadSafeMutableSet;
 import java.util.Collection;
-import java.util.Set;
 import java.util.regex.Pattern;
 
 /**
@@ -74,11 +74,12 @@ class LetExpression extends QueryExpression {
       return env.immediateFailedFuture(
           new QueryException(this, "invalid variable name '" + varName + "' in let expression"));
     }
-    QueryTaskFuture<Set<T>> varValueFuture = QueryUtil.evalAll(env, context, varExpr);
-    Function<Set<T>, QueryTaskFuture<Void>> evalBodyAsyncFunction =
-        new Function<Set<T>, QueryTaskFuture<Void>>() {
+    QueryTaskFuture<ThreadSafeMutableSet<T>> varValueFuture =
+        QueryUtil.evalAll(env, context, varExpr);
+    Function<ThreadSafeMutableSet<T>, QueryTaskFuture<Void>> evalBodyAsyncFunction =
+        new Function<ThreadSafeMutableSet<T>, QueryTaskFuture<Void>>() {
           @Override
-          public QueryTaskFuture<Void> apply(Set<T> varValue) {
+          public QueryTaskFuture<Void> apply(ThreadSafeMutableSet<T> varValue) {
             VariableContext<T> bodyContext = VariableContext.with(context, varName, varValue);
             return env.eval(bodyExpr, bodyContext, callback);
           }