diff --git a/changes/routerparse_maxima b/changes/routerparse_maxima
new file mode 100644
index 0000000000..340f2c3c2d
--- /dev/null
+++ b/changes/routerparse_maxima
@@ -0,0 +1,4 @@
+  o Minor bugfixes
+    - Check for and reject overly long directory certificates and
+      directory tokens before they have a chance to hit any
+      assertions. Bugfix on 0.2.1.28. Found by doorss.
diff --git a/src/or/routerparse.c b/src/or/routerparse.c
index 08f81d9f76..5ceb298b8b 100644
--- a/src/or/routerparse.c
+++ b/src/or/routerparse.c
@@ -1720,6 +1720,10 @@ extrainfo_parse_entry_from_string(const char *s, const char *end,
 authority_cert_t *
 authority_cert_parse_from_string(const char *s, const char **end_of_string)
 {
+  /** Reject any certificate at least this big; it is probably an overflow, an
+   * attack, a bug, or some other nonsense. */
+#define MAX_CERT_SIZE (128*1024)
+
   authority_cert_t *cert = NULL, *old_cert;
   smartlist_t *tokens = NULL;
   char digest[DIGEST_LEN];
@@ -1747,6 +1751,12 @@ authority_cert_parse_from_string(const char *s, const char **end_of_string)
   ++eos;
   len = eos - s;
 
+  if (len > MAX_CERT_SIZE) {
+    log_warn(LD_DIR, "Certificate is far too big (at %lu bytes long); "
+             "rejecting", (unsigned long)len);
+    return NULL;
+  }
+
   tokens = smartlist_create();
   area = memarea_new();
   if (tokenize_string(area,s, eos, tokens, dir_key_certificate_table, 0) < 0) {
@@ -3818,6 +3828,9 @@ get_next_token(memarea_t *area,
   /** Reject any object at least this big; it is probably an overflow, an
    * attack, a bug, or some other nonsense. */
 #define MAX_UNPARSED_OBJECT_SIZE (128*1024)
+  /** Reject any line at least this big; it is probably an overflow, an
+   * attack, a bug, or some other nonsense. */
+#define MAX_LINE_LENGTH (128*1024)
 
   const char *next, *eol, *obstart;
   size_t obname_len;
@@ -3837,6 +3850,10 @@ get_next_token(memarea_t *area,
   eol = memchr(*s, '\n', eos-*s);
   if (!eol)
     eol = eos;
+  if (eol - *s > MAX_LINE_LENGTH) {
+    RET_ERR("Line far too long");
+  }
+
   next = find_whitespace_eos(*s, eol);
 
   if (!strcmp_len(*s, "opt", next-*s)) {