diff --git a/activitypub.c b/activitypub.c
index 7f642b9..6c8772d 100644
--- a/activitypub.c
+++ b/activitypub.c
@@ -498,7 +498,7 @@ xs_dict *msg_base(snac *snac, const char *type, const char *id,
 
     /* generated values */
     if (date && strcmp(date, "@now") == 0) {
-        published = xs_str_utctime(0, "%Y-%m-%dT%H:%M:%SZ");
+        published = xs_str_utctime(0, ISO_DATE_SPEC);
         date = published;
     }
 
@@ -959,7 +959,7 @@ xs_dict *msg_question(snac *user, const char *content, const xs_list *opts, int
 
     /* set the end time */
     time_t t = time(NULL) + end_secs;
-    xs *et = xs_str_utctime(t, "%Y-%m-%dT%H:%M:%SZ");
+    xs *et = xs_str_utctime(t, ISO_DATE_SPEC);
 
     msg = xs_dict_append(msg, "endTime", et);
 
@@ -1234,7 +1234,7 @@ int process_input_message(snac *snac, xs_dict *msg, xs_dict *req)
 
             if (xs_is_null(xs_dict_get(f_msg, "published"))) {
                 /* add a date if it doesn't include one (Mastodon) */
-                xs *date = xs_str_utctime(0, "%Y-%m-%dT%H:%M:%SZ");
+                xs *date = xs_str_utctime(0, ISO_DATE_SPEC);
                 f_msg = xs_dict_set(f_msg, "published", date);
             }
 
diff --git a/data.c b/data.c
index fa079cc..303b534 100644
--- a/data.c
+++ b/data.c
@@ -1688,7 +1688,7 @@ void notify_add(snac *snac, const char *type, const char *utype,
 {
     xs *ntid = tid(0);
     xs *fn   = xs_fmt("%s/notify/", snac->basedir);
-    xs *date = xs_str_utctime(0, "%Y-%m-%dT%H:%M:%SZ");
+    xs *date = xs_str_utctime(0, ISO_DATE_SPEC);
     FILE *f;
 
     /* create the directory */
diff --git a/html.c b/html.c
index 83a2b13..ea00ac1 100644
--- a/html.c
+++ b/html.c
@@ -1756,7 +1756,7 @@ int html_post_handler(const xs_dict *req, const char *q_path,
                     }
 
                     /* set the updated field */
-                    xs *updated = xs_str_utctime(0, "%Y-%m-%dT%H:%M:%SZ");
+                    xs *updated = xs_str_utctime(0, ISO_DATE_SPEC);
                     msg = xs_dict_set(msg, "updated", updated);
 
                     /* overwrite object, not updating the indexes */
diff --git a/mastoapi.c b/mastoapi.c
index dc8320d..feeb06f 100644
--- a/mastoapi.c
+++ b/mastoapi.c
@@ -524,7 +524,7 @@ xs_dict *mastoapi_account(const xs_dict *actor)
         acct = xs_dict_append(acct, "created_at", pub);
     else {
         /* unset created_at crashes Tusky, so lie like a mf */
-        xs *date = xs_str_utctime(0, "%Y-%m-%dT%H:%M:%SZ");
+        xs *date = xs_str_utctime(0, ISO_DATE_SPEC);
         acct = xs_dict_append(acct, "created_at", date);
     }
 
diff --git a/snac.h b/snac.h
index 77825dc..bf8948b 100644
--- a/snac.h
+++ b/snac.h
@@ -9,6 +9,8 @@
 
 #define DIR_PERM 02770
 
+#define ISO_DATE_SPEC "%Y-%m-%dT%H:%M:%SZ"
+
 extern double disk_layout;
 extern d_char *srv_basedir;
 extern d_char *srv_config;
diff --git a/utils.c b/utils.c
index 8594d84..7d51b82 100644
--- a/utils.c
+++ b/utils.c
@@ -218,7 +218,7 @@ int adduser(const char *uid)
 {
     snac snac;
     xs *config = xs_dict_new();
-    xs *date = xs_str_utctime(0, "%Y-%m-%dT%H:%M:%SZ");
+    xs *date = xs_str_utctime(0, ISO_DATE_SPEC);
     xs *pwd = NULL;
     xs *pwd_f = NULL;
     xs *key = NULL;