diff --git a/tests/time_test.cpp b/tests/time_test.cpp
index f0ad937..5f802aa 100644
--- a/tests/time_test.cpp
+++ b/tests/time_test.cpp
@@ -168,6 +168,8 @@
 }
 
 TEST(time, mktime_EOVERFLOW) {
+  setenv("TZ", "UTC", 1);
+
   struct tm t;
   memset(&t, 0, sizeof(tm));