diff --git a/mfbt/tests/TestSplayTree.cpp b/mfbt/tests/TestSplayTree.cpp
index 0fd37b69f01..31b3bb3f21a 100644
--- a/mfbt/tests/TestSplayTree.cpp
+++ b/mfbt/tests/TestSplayTree.cpp
@@ -7,6 +7,7 @@
 #include "mozilla/ArrayUtils.h"
 #include "mozilla/Assertions.h"
 #include "mozilla/SplayTree.h"
+#include "mozilla/unused.h"
 
 using mozilla::SplayTree;
 using mozilla::SplayTreeNode;
@@ -118,6 +119,8 @@ static SplayTree<SplayNoCopy, SplayNoCopy> testNoCopy;
 int
 main()
 {
+  mozilla::unused << testNoCopy;
+
   SplayTree<SplayInt, SplayInt> tree;
 
   MOZ_RELEASE_ASSERT(tree.empty());