diff --git a/tests/extensions.cpp b/tests/extensions.cpp
index 62cab82..45af7cb 100644
--- a/tests/extensions.cpp
+++ b/tests/extensions.cpp
@@ -8,8 +8,8 @@
   REQUIRE(e);
 
 TEST_CASE("Map extensions", "[extensions.map]") {
-  auto mul2 = [](auto a) { return a * 2; };
-  auto ret_void = [](auto a) {};
+  auto mul2 = [](int a) { return a * 2; };
+  auto ret_void = [](int a) {};
 
   {
     tl::expected<int, int> e = 21;