diff --git a/src/backend/commands/variable.c b/src/backend/commands/variable.c
index a3448e4c785..c9574dfa937 100644
--- a/src/backend/commands/variable.c
+++ b/src/backend/commands/variable.c
@@ -388,6 +388,13 @@ check_timezone(char **newval, void **extra, GucSource source)
 		}
 	}
 
+	/* Test for failure in pg_tzset_offset, which we assume is out-of-range */
+	if (!myextra.session_timezone)
+	{
+		GUC_check_errdetail("UTC timezone offset is out of range.");
+		return false;
+	}
+
 	/*
 	 * Prepare the canonical string to return.  GUC wants it malloc'd.
 	 *
diff --git a/src/timezone/pgtz.c b/src/timezone/pgtz.c
index 008acb395b9..c2f52ed3dcb 100644
--- a/src/timezone/pgtz.c
+++ b/src/timezone/pgtz.c
@@ -1333,6 +1333,9 @@ pg_tzset(const char *name)
  * The GMT offset is specified in seconds, positive values meaning west of
  * Greenwich (ie, POSIX not ISO sign convention).  However, we use ISO
  * sign convention in the displayable abbreviation for the zone.
+ *
+ * Caution: this can fail (return NULL) if the specified offset is outside
+ * the range allowed by the zic library.
  */
 pg_tz *
 pg_tzset_offset(long gmtoffset)