diff --git a/test/source/io.cpp b/test/source/io.cpp
index b680be7..89506b1 100644
--- a/test/source/io.cpp
+++ b/test/source/io.cpp
@@ -92,6 +92,10 @@
     EXPECT_EQ(5, return_fd);
     EXPECT_EQ(EPOLLIN, return_revents);
 
+    io.set_callback(std::bind([]() {}));
+    EXPECT_EQ(0, handler(nullptr, 5, EPOLLIN, &io));
+    EXPECT_EQ(1, completions);
+
     expect_destruct();
 }