diff --git a/kernel/modtools.h b/kernel/modtools.h
index 40d7159e5..8ec70f0e9 100644
--- a/kernel/modtools.h
+++ b/kernel/modtools.h
@@ -78,6 +78,8 @@ struct ModIndex : public RTLIL::Monitor
 
 	SigMap sigmap;
 private:
+	friend class ModIndexTest;
+	FRIEND_TEST(ModIndexTest, swap);
 	struct sigbit_pointer_hash
 	{
 		std::size_t operator()(const Yosys::RTLIL::SigBit& s) const noexcept
diff --git a/tests/unit/kernel/modindexTest.cc b/tests/unit/kernel/modindexTest.cc
index 1921c9a93..b972cb165 100644
--- a/tests/unit/kernel/modindexTest.cc
+++ b/tests/unit/kernel/modindexTest.cc
@@ -5,7 +5,7 @@
 
 YOSYS_NAMESPACE_BEGIN
 
-TEST(ModIndexSwapTest, has)
+TEST(ModIndexTest, swap)
 {
     Design* d = new Design;
     Module* m = d->addModule("$m");
@@ -26,7 +26,7 @@ TEST(ModIndexSwapTest, has)
     }
 }
 
-TEST(ModIndexDeleteTest, has)
+TEST(ModIndexTest, modify)
 {
     if (log_files.empty()) log_files.emplace_back(stdout);
     Design* d = new Design;