diff --git a/libc/tzcode/localtime.c b/libc/tzcode/localtime.c
index 28d13f4..29f605c 100644
--- a/libc/tzcode/localtime.c
+++ b/libc/tzcode/localtime.c
@@ -1257,6 +1257,7 @@
         lclptr->ttis[0].tt_gmtoff = 0;
         lclptr->ttis[0].tt_abbrind = 0;
         (void) strcpy(lclptr->chars, gmt);
+        lclptr->defaulttype = 0;
     } else if (tzload(name, lclptr, TRUE) != 0)
         if (name[0] == ':' || tzparse(name, lclptr, FALSE) != 0)
             (void) gmtload(lclptr);
diff --git a/tests/time_test.cpp b/tests/time_test.cpp
index 7a551b4..e0231b1 100644
--- a/tests/time_test.cpp
+++ b/tests/time_test.cpp
@@ -71,6 +71,30 @@
   ASSERT_EQ(0, pthread_join(t, &result));
 }
 
+TEST(time, mktime_empty_TZ) {
+  // tzcode used to have a bug where it didn't reinitialize some internal state.
+
+  // Choose a time where DST is set.
+  struct tm t;
+  memset(&t, 0, sizeof(tm));
+  t.tm_year = 1980 - 1900;
+  t.tm_mon = 6;
+  t.tm_mday = 2;
+
+  setenv("TZ", "America/Los_Angeles", 1);
+  tzset();
+  ASSERT_EQ(static_cast<time_t>(331372800U), mktime(&t));
+
+  memset(&t, 0, sizeof(tm));
+  t.tm_year = 1980 - 1900;
+  t.tm_mon = 6;
+  t.tm_mday = 2;
+
+  setenv("TZ", "", 1); // Implies UTC.
+  tzset();
+  ASSERT_EQ(static_cast<time_t>(331344000U), mktime(&t));
+}
+
 TEST(time, mktime_10310929) {
   struct tm t;
   memset(&t, 0, sizeof(tm));