diff --git a/src/common/util.c b/src/common/util.c
index c44a4aa3b1..e7059a5bd9 100644
--- a/src/common/util.c
+++ b/src/common/util.c
@@ -1430,6 +1430,26 @@ format_iso_time(char *buf, time_t t)
   strftime(buf, ISO_TIME_LEN+1, "%Y-%m-%d %H:%M:%S", tor_gmtime_r(&t, &tm));
 }
 
+/** As format_iso_time, but use the yyyy-mm-ddThh:mm:ss format to avoid
+ * embedding an internal space. */
+void
+format_iso_time_nospace(char *buf, time_t t)
+{
+  format_iso_time(buf, t);
+  buf[10] = 'T';
+}
+
+/** As format_iso_time_nospace, but include microseconds in decimal
+ * fixed-point format.  Requires that buf be at least ISO_TIME_USEC_LEN+1
+ * bytes long. */
+void
+format_iso_time_nospace_usec(char *buf, const struct timeval *tv)
+{
+  tor_assert(tv);
+  format_iso_time_nospace(buf, tv->tv_sec);
+  tor_snprintf(buf+ISO_TIME_LEN, 8, ".%06d", (int)tv->tv_usec);
+}
+
 /** Given an ISO-formatted UTC time value (after the epoch) in <b>cp</b>,
  * parse it and store its value in *<b>t</b>.  Return 0 on success, -1 on
  * failure.  Ignore extraneous stuff in <b>cp</b> separated by whitespace from
diff --git a/src/common/util.h b/src/common/util.h
index 77ed1ca5ee..bd471e3816 100644
--- a/src/common/util.h
+++ b/src/common/util.h
@@ -242,8 +242,11 @@ time_t tor_timegm(struct tm *tm);
 void format_rfc1123_time(char *buf, time_t t);
 int parse_rfc1123_time(const char *buf, time_t *t);
 #define ISO_TIME_LEN 19
+#define ISO_TIME_USEC_LEN (ISO_TIME_LEN+7)
 void format_local_iso_time(char *buf, time_t t);
 void format_iso_time(char *buf, time_t t);
+void format_iso_time_nospace(char *buf, time_t t);
+void format_iso_time_nospace_usec(char *buf, const struct timeval *tv);
 int parse_iso_time(const char *buf, time_t *t);
 int parse_http_time(const char *buf, struct tm *tm);
 int format_time_interval(char *out, size_t out_len, long interval);
diff --git a/src/or/control.c b/src/or/control.c
index e15adbd8e8..364cf9905c 100644
--- a/src/or/control.c
+++ b/src/or/control.c
@@ -1853,10 +1853,10 @@ circuit_describe_status_for_controller(origin_circuit_t *circ)
 
   {
     char *time_created_arg = NULL;
+    char tbuf[ISO_TIME_USEC_LEN+1];
+    format_iso_time_nospace_usec(tbuf, &circ->_base.timestamp_created);
 
-    tor_asprintf(&time_created_arg, "TIME_CREATED=%ld,%ld",
-                 circ->_base.timestamp_created.tv_sec,
-                 circ->_base.timestamp_created.tv_usec);
+    tor_asprintf(&time_created_arg, "TIME_CREATED=%s", tbuf);
 
     smartlist_add(descparts, time_created_arg);
   }
diff --git a/src/test/test_util.c b/src/test/test_util.c
index 64bf52e7b1..d549e235b6 100644
--- a/src/test/test_util.c
+++ b/src/test/test_util.c
@@ -19,9 +19,10 @@ test_util_time(void)
 {
   struct timeval start, end;
   struct tm a_time;
-  char timestr[RFC1123_TIME_LEN+1];
+  char timestr[128];
   time_t t_res;
   int i;
+  struct timeval tv;
 
   start.tv_sec = 5;
   start.tv_usec = 5000;
@@ -83,6 +84,24 @@ test_util_time(void)
   /* We might've timewarped a little. */
   tt_int_op(tv_udiff(&start, &end), >=, -5000);
 
+  /* Now let's check some format_iso_time variants */
+  tv.tv_sec = (time_t)1326296338;
+  tv.tv_usec = 3060;
+  format_iso_time(timestr, tv.tv_sec);
+  test_streq("2012-01-11 15:38:58", timestr);
+  /* The output of format_local_iso_time will vary by timezone, and setting
+     our timezone for testing purposes would be a nontrivial flaky pain.
+     Skip this test for now.
+  format_local_iso_time(timestr, tv.tv_sec);
+  test_streq("2012-01-11 10:38:58", timestr);
+  */
+  format_iso_time_nospace(timestr, tv.tv_sec);
+  test_streq("2012-01-11T15:38:58", timestr);
+  test_eq(strlen(timestr), ISO_TIME_LEN);
+  format_iso_time_nospace_usec(timestr, &tv);
+  test_streq("2012-01-11T15:38:58.003060", timestr);
+  test_eq(strlen(timestr), ISO_TIME_USEC_LEN);
+
  done:
   ;
 }