diff --git a/tests/time_test.cpp b/tests/time_test.cpp
index 378b4ac..74d691d 100644
--- a/tests/time_test.cpp
+++ b/tests/time_test.cpp
@@ -1005,3 +1005,7 @@
   GTEST_SKIP() << "glibc doesn't have timespec_get until 2.21";
 #endif
 }
+
+TEST(time, difftime) {
+  ASSERT_EQ(1.0, difftime(1, 0));
+}