diff --git a/CHANGES b/CHANGES
index 322f65d400..f232e80c0f 100644
--- a/CHANGES
+++ b/CHANGES
@@ -1,3 +1,6 @@
+4855.	[bug]		isc_time_formatshorttimestamp produced incorrect
+			output. [RT #46938]
+
 4854.	[bug]		query_synthcnamewildcard should stop generating the
 			response if query_synthwildcard fails. [RT #46939]
 
diff --git a/lib/isc/tests/time_test.c b/lib/isc/tests/time_test.c
index 12a8743d20..d20ed0fabe 100644
--- a/lib/isc/tests/time_test.c
+++ b/lib/isc/tests/time_test.c
@@ -182,6 +182,37 @@ ATF_TC_BODY(isc_time_formatISO8601Lms, tc) {
 	ATF_CHECK_STREQ(buf, "2015-12-13T01:46:40.123");
 }
 
+ATF_TC(isc_time_formatshorttimestamp);
+ATF_TC_HEAD(isc_time_formatshorttimestamp, tc) {
+	atf_tc_set_md_var(tc, "descr",
+			  "print UTC time as yyyymmddhhmmsssss");
+}
+ATF_TC_BODY(isc_time_formatshorttimestamp, tc) {
+	isc_result_t result;
+	isc_time_t t;
+	char buf[64];
+
+	setenv("TZ", "PST8PDT", 1);
+	result = isc_time_now(&t);
+	ATF_REQUIRE_EQ(result, ISC_R_SUCCESS);
+
+	/* check formatting: yyyymmddhhmmsssss */
+	memset(buf, 'X', sizeof(buf));
+	isc_time_formatshorttimestamp(&t, buf, sizeof(buf));
+	ATF_CHECK_EQ(strlen(buf), 17);
+
+	/* check time conversion correctness */
+	memset(buf, 'X', sizeof(buf));
+	isc_time_settoepoch(&t);
+	isc_time_formatshorttimestamp(&t, buf, sizeof(buf));
+	ATF_CHECK_STREQ(buf, "19700101000000000");
+
+	memset(buf, 'X', sizeof(buf));
+	isc_time_set(&t, 1450000000, 123000000);
+	isc_time_formatshorttimestamp(&t, buf, sizeof(buf));
+	ATF_CHECK_STREQ(buf, "20151213094640123");
+}
+
 /*
  * Main
  */
@@ -191,6 +222,6 @@ ATF_TP_ADD_TCS(tp) {
 	ATF_TP_ADD_TC(tp, isc_time_formatISO8601ms);
 	ATF_TP_ADD_TC(tp, isc_time_formatISO8601L);
 	ATF_TP_ADD_TC(tp, isc_time_formatISO8601Lms);
+	ATF_TP_ADD_TC(tp, isc_time_formatshorttimestamp);
 	return (atf_no_error());
 }
-
diff --git a/lib/isc/unix/time.c b/lib/isc/unix/time.c
index 589225cac2..eccae669f4 100644
--- a/lib/isc/unix/time.c
+++ b/lib/isc/unix/time.c
@@ -552,6 +552,9 @@ isc_time_formatshorttimestamp(const isc_time_t *t, char *buf, unsigned int len)
 	struct tm tm;
 #endif
 
+	REQUIRE(t != NULL);
+	INSIST(t->nanoseconds < NS_PER_S);
+	REQUIRE(buf != NULL);
 	REQUIRE(len > 0);
 
 	now = (time_t)t->seconds;
@@ -562,7 +565,6 @@ isc_time_formatshorttimestamp(const isc_time_t *t, char *buf, unsigned int len)
 #endif
 	INSIST(flen < len);
 	if (flen > 0U && len - flen >= 5) {
-		flen -= 1; /* rewind one character (Z) */
 		snprintf(buf + flen, len - flen, "%03u",
 			 t->nanoseconds / NS_PER_MS);
 	}
diff --git a/lib/isc/win32/time.c b/lib/isc/win32/time.c
index a4b6e92354..fa00293984 100644
--- a/lib/isc/win32/time.c
+++ b/lib/isc/win32/time.c
@@ -442,7 +442,10 @@ isc_time_formatshorttimestamp(const isc_time_t *t, char *buf, unsigned int len)
 
 	/* strtime() format: "%Y%m%d%H%M%SSSS" */
 
+	REQUIRE(t != NULL);
+	REQUIRE(buf != NULL);
 	REQUIRE(len > 0);
+
 	if (FileTimeToSystemTime(&t->absolute, &st)) {
 		GetDateFormat(LOCALE_NEUTRAL, 0, &st, "yyyyMMdd",
 			      DateBuf, 50);