diff --git a/lib/isc/include/isc/result.h b/lib/isc/include/isc/result.h

index 0389efa..149cde5 100644

--- a/lib/isc/include/isc/result.h

+++ b/lib/isc/include/isc/result.h

@@ -89,7 +89,8 @@

 #define ISC_R_DISCFULL			67	/*%< disc full */

 #define ISC_R_DEFAULT			68	/*%< default */

 #define ISC_R_IPV4PREFIX		69	/*%< IPv4 prefix */

-#define ISC_R_NRESULTS 			70

+#define ISC_R_TIMESHIFTED               70      /*%< system time changed */

+#define ISC_R_NRESULTS 			71

 ISC_LANG_BEGINDECLS

diff --git a/lib/isc/include/isc/util.h b/lib/isc/include/isc/util.h

index 973c348..cceeb5e 100644

--- a/lib/isc/include/isc/util.h

+++ b/lib/isc/include/isc/util.h

@@ -289,6 +289,10 @@ extern void mock_assert(const int result, const char* const expression,

  * Time

  */

 #define TIME_NOW(tp) 	RUNTIME_CHECK(isc_time_now((tp)) == ISC_R_SUCCESS)

+#ifdef CLOCK_BOOTTIME

+#define TIME_MONOTONIC(tp) 	RUNTIME_CHECK(isc_time_boottime((tp)) == ISC_R_SUCCESS)

+#endif

+

 /*%

  * Alignment

diff --git a/lib/isc/result.c b/lib/isc/result.c

index a9db132..f33fc6b 100644

--- a/lib/isc/result.c

+++ b/lib/isc/result.c

@@ -105,6 +105,7 @@ static const char *description[ISC_R_NRESULTS] = {

 	"disc full",				/*%< 67 */

 	"default",				/*%< 68 */

 	"IPv4 prefix",				/*%< 69 */

+	"time changed",                         /*%< 70 */

 };

 static const char *identifier[ISC_R_NRESULTS] = {

@@ -178,6 +179,7 @@ static const char *identifier[ISC_R_NRESULTS] = {

 	"ISC_R_DISCFULL",

 	"ISC_R_DEFAULT",

 	"ISC_R_IPV4PREFIX",

+	"ISC_R_TIMESHIFTED",

 };

 #define ISC_RESULT_RESULTSET			2

diff --git a/lib/isc/unix/app.c b/lib/isc/unix/app.c

index a6e9882..286fe95 100644

--- a/lib/isc/unix/app.c

+++ b/lib/isc/unix/app.c

@@ -442,15 +442,47 @@ isc__app_ctxonrun(isc_appctx_t *ctx0, isc_mem_t *mctx, isc_task_t *task,

 static isc_result_t

 evloop(isc__appctx_t *ctx) {

 	isc_result_t result;

+        isc_time_t now;

+#ifdef CLOCK_BOOTTIME

+        isc_time_t monotonic;

+        isc_uint64_t diff  = 0;

+#else

+        isc_time_t prev;

+        TIME_NOW(&prev;;

+#endif

 	while (!ctx->want_shutdown) {

 		int n;

-		isc_time_t when, now;

+		isc_time_t when;

 		struct timeval tv, *tvp;

 		isc_socketwait_t *swait;

 		bool readytasks;

 		bool call_timer_dispatch = false;

+                uint64_t us; 

+

+#ifdef CLOCK_BOOTTIME

+                // TBD macros for following three lines

+                TIME_NOW(&now;;

+                TIME_MONOTONIC(&monotonic);

+                INSIST(now.seconds > monotonic.seconds)

+                us = isc_time_microdiff (&now, &monotonic);

+                if (us < diff){

+                  us = diff - us;

+                  if (us > 1000000){ // ignoring shifts less than one second

+                    return ISC_R_TIMESHIFTED;

+                  };

+                  diff = isc_time_microdiff (&now, &monotonic);

+                } else {

+                  diff = isc_time_microdiff (&now, &monotonic);

+                  // not implemented

+                }

+#else

+                TIME_NOW(&now;;

+                if (isc_time_compare (&now, &prev) < 0)

+                  return ISC_R_TIMESHIFTED;

+                TIME_NOW(&prev;;

+#endif

 		/*

 		 * Check the reload (or suspend) case first for exiting the

 		 * loop as fast as possible in case:

@@ -475,7 +507,6 @@ evloop(isc__appctx_t *ctx) {

 			if (result != ISC_R_SUCCESS)

 				tvp = NULL;

 			else {

-				uint64_t us;

 				TIME_NOW(&now;;

 				us = isc_time_microdiff(&when, &now;;

diff --git a/lib/isc/unix/include/isc/time.h b/lib/isc/unix/include/isc/time.h

index b864c29..5dd43c9 100644

--- a/lib/isc/unix/include/isc/time.h

+++ b/lib/isc/unix/include/isc/time.h

@@ -132,6 +132,26 @@ isc_time_isepoch(const isc_time_t *t);

  *\li	't' is a valid pointer.

  */

+#ifdef CLOCK_BOOTTIME

+isc_result_t

+isc_time_boottime(isc_time_t *t);

+/*%<

+ * Set 't' to monotonic time from previous boot

+ * it's not affected by system time change. It also

+ * includes the time system was suspended

+ *

+ * Requires:

+ *\li	't' is a valid pointer.

+ *

+ * Returns:

+ *

+ *\li	Success

+ *\li	Unexpected error

+ *		Getting the time from the system failed.

+ */

+#endif /* CLOCK_BOOTTIME */

+ 

+

 isc_result_t

 isc_time_now(isc_time_t *t);

 /*%<

diff --git a/lib/isc/unix/time.c b/lib/isc/unix/time.c

index 8edc9df..fe0bb91 100644

--- a/lib/isc/unix/time.c

+++ b/lib/isc/unix/time.c

@@ -498,3 +498,25 @@ isc_time_formatISO8601ms(const isc_time_t *t, char *buf, unsigned int len) {

 			 t->nanoseconds / NS_PER_MS);

 	}

 }

+

+

+#ifdef CLOCK_BOOTTIME

+isc_result_t

+isc_time_boottime(isc_time_t *t) {

+  struct timespec ts;

+  

+  char strbuf[ISC_STRERRORSIZE];

+

+  if (clock_gettime (CLOCK_BOOTTIME, &ts) != 0){

+    isc__strerror(errno, strbuf, sizeof(strbuf));

+    UNEXPECTED_ERROR(__FILE__, __LINE__, "%s", strbuf);

+    return (ISC_R_UNEXPECTED);    

+  }

+

+  t->seconds = ts.tv_sec;

+  t->nanoseconds = ts.tv_nsec;

+

+  return (ISC_R_SUCCESS);

+  

+};

+#endif