diff --git a/src/libCom/test/epicsTimeZoneTest.c b/src/libCom/test/epicsTimeZoneTest.c
index dd12b1acf..685295fc4 100644
--- a/src/libCom/test/epicsTimeZoneTest.c
+++ b/src/libCom/test/epicsTimeZoneTest.c
@@ -17,15 +17,9 @@
 #endif
 
 static
-void setTZ(const char *base, const char *dst, int offset)
+void setTZ(const char *tz)
 {
-    char tz[20];
-    if(offset!=0 || dst)
-        sprintf(tz, "%s%d%s", base, offset/3600, dst);
-    else
-        sprintf(tz, "%s", base);
-    testDiag("TZ=\"%s\"", tz);
-
+    testDiag("TZ = \"%s\"", tz);
     epicsEnvSet("TZ", tz);
     tzset();
 }
@@ -86,32 +80,52 @@ void test_gmtime(time_t T, int sec, int min, int hour,
 
 MAIN(epicsTimeZoneTest)
 {
-    testPlan(80);
+    testPlan(160);
     /* 1445259616
      *  Mon Oct 19 09:00:16 2015 EDT
      *  Mon Oct 19 08:00:16 2015 CDT
+     *  Mon Oct 19 03:00:16 2015 HST  (no dst)
      *  Mon Oct 19 13:00:16 2015 UTC
      */
     testDiag("POSIX 1445259616");
-    setTZ("EST", "EDT", 5*3600);
-    test_localtime(1445259616ul, 16, 0, 9, 19, 9, 2015, 1, 291, 1);
-    setTZ("CST", "CDT", 6*3600);
-    test_localtime(1445259616ul, 16, 0, 8, 19, 9, 2015, 1, 291, 1);
-    setTZ("UTC", NULL, 0);
+    setTZ("EST5EDT");
+    test_localtime(1445259616ul, 16, 0, 9,  19, 9, 2015, 1, 291, 1);
+    test_gmtime   (1445259616ul, 16, 0, 13, 19, 9, 2015, 1, 291, 0);
+    setTZ("CST6CDT");
+    test_localtime(1445259616ul, 16, 0, 8,  19, 9, 2015, 1, 291, 1);
+    test_gmtime   (1445259616ul, 16, 0, 13, 19, 9, 2015, 1, 291, 0);
+#if defined(__rtems__)
+    setTZ("HST10HST10");
+#else
+    setTZ("HST10");
+#endif
+    test_localtime(1445259616ul, 16, 0, 3,  19, 9, 2015, 1, 291, 0);
+    test_gmtime   (1445259616ul, 16, 0, 13, 19, 9, 2015, 1, 291, 0);
+    setTZ("UTC0");
     test_localtime(1445259616ul, 16, 0, 13, 19, 9, 2015, 1, 291, 0);
-    test_gmtime(1445259616ul, 16, 0, 13, 19, 9, 2015, 1, 291, 0);
+    test_gmtime   (1445259616ul, 16, 0, 13, 19, 9, 2015, 1, 291, 0);
     /* 1421244931
      *  Wed Jan 14 09:15:31 2015 EST
      *  Wed Jan 14 08:15:31 2015 CST
+     *  Wed Jan 14 04:15:31 2015 HST
      *  Wed Jan 14 14:15:31 2015 UTC
      */
     testDiag("POSIX 1421244931");
-    setTZ("EST", "EDT", 5*3600);
-    test_localtime(1421244931ul, 31, 15, 9, 14, 0, 2015, 3, 13, 0);
-    setTZ("CST", "CDT", 6*3600);
-    test_localtime(1421244931ul, 31, 15, 8, 14, 0, 2015, 3, 13, 0);
-    setTZ("UTC", NULL, 0);
+    setTZ("EST5EDT");
+    test_localtime(1421244931ul, 31, 15,  9, 14, 0, 2015, 3, 13, 0);
+    test_gmtime   (1421244931ul, 31, 15, 14, 14, 0, 2015, 3, 13, 0);
+    setTZ("CST6CDT");
+    test_localtime(1421244931ul, 31, 15,  8, 14, 0, 2015, 3, 13, 0);
+    test_gmtime   (1421244931ul, 31, 15, 14, 14, 0, 2015, 3, 13, 0);
+#if defined(__rtems__)
+    setTZ("HST10HST10");
+#else
+    setTZ("HST10");
+#endif
+    test_localtime(1421244931ul, 31, 15,  4, 14, 0, 2015, 3, 13, 0);
+    test_gmtime   (1421244931ul, 31, 15, 14, 14, 0, 2015, 3, 13, 0);
+    setTZ("UTC0");
     test_localtime(1421244931ul, 31, 15, 14, 14, 0, 2015, 3, 13, 0);
-    test_gmtime(1421244931ul, 31, 15, 14, 14, 0, 2015, 3, 13, 0);
+    test_gmtime   (1421244931ul, 31, 15, 14, 14, 0, 2015, 3, 13, 0);
     return testDone();
 }