diff --git a/tests/mts/bpf_existence_test.cpp b/tests/mts/bpf_existence_test.cpp
index ac8096c..142e013 100644
--- a/tests/mts/bpf_existence_test.cpp
+++ b/tests/mts/bpf_existence_test.cpp
@@ -92,7 +92,7 @@
     a->insert(b.begin(), b.end());
 }
 
-void removeAll(set<string>* a, const set<string> b) {
+void removeAll(set<string>* a, const set<string>& b) {
     for (const auto& toRemove : b) {
         a->erase(toRemove);
     }