diff --git a/changes/bug9047 b/changes/bug9047
new file mode 100644
index 0000000000..497f0d3372
--- /dev/null
+++ b/changes/bug9047
@@ -0,0 +1,6 @@
+  o Minor bugfixes:
+    - If for some reason we fail to write a microdescriptor while
+      rebuilding the cache, do not let the annotations from that
+      microdescriptor linger in the cache file, and do not let the
+      microdescriptor stay recorded as present in its old location.
+      Fixes bug 9047; bugfix on 0.2.2.6-alpha.
diff --git a/src/common/compat.c b/src/common/compat.c
index c97a4545c9..24b44fb055 100644
--- a/src/common/compat.c
+++ b/src/common/compat.c
@@ -900,6 +900,18 @@ tor_fd_seekend(int fd)
 #endif
 }
 
+/** Move <b>fd</b> to position <b>pos</b> in the file. Return -1 on error, 0
+ * on success. */
+int
+tor_fd_setpos(int fd, off_t pos)
+{
+#ifdef _WIN32
+  return _lseek(fd, pos, SEEK_SET) < 0 ? -1 : 0;
+#else
+  return lseek(fd, pos, SEEK_SET) < 0 ? -1 : 0;
+#endif
+}
+
 #undef DEBUG_SOCKET_COUNTING
 #ifdef DEBUG_SOCKET_COUNTING
 /** A bitarray of all fds that should be passed to tor_socket_close(). Only
diff --git a/src/common/compat.h b/src/common/compat.h
index f0a34aae41..8ab7190526 100644
--- a/src/common/compat.h
+++ b/src/common/compat.h
@@ -411,6 +411,7 @@ tor_lockfile_t *tor_lockfile_lock(const char *filename, int blocking,
 void tor_lockfile_unlock(tor_lockfile_t *lockfile);
 
 off_t tor_fd_getpos(int fd);
+int tor_fd_setpos(int fd, off_t pos);
 int tor_fd_seekend(int fd);
 
 #ifdef _WIN32
diff --git a/src/or/microdesc.c b/src/or/microdesc.c
index 05e3b41815..b93bd83af5 100644
--- a/src/or/microdesc.c
+++ b/src/or/microdesc.c
@@ -74,7 +74,7 @@ static ssize_t
 dump_microdescriptor(int fd, microdesc_t *md, size_t *annotation_len_out)
 {
   ssize_t r = 0;
-  size_t written;
+  ssize_t written;
   if (md->body == NULL) {
     *annotation_len_out = 0;
     return 0;
@@ -99,10 +99,10 @@ dump_microdescriptor(int fd, microdesc_t *md, size_t *annotation_len_out)
 
   md->off = tor_fd_getpos(fd);
   written = write_all(fd, md->body, md->bodylen, 0);
-  if (written != md->bodylen) {
+  if (written != (ssize_t)md->bodylen) {
     log_warn(LD_DIR,
-             "Couldn't dump microdescriptor (wrote %lu out of %lu): %s",
-             (unsigned long)written, (unsigned long)md->bodylen,
+             "Couldn't dump microdescriptor (wrote %ld out of %lu): %s",
+             (long)written, (unsigned long)md->bodylen,
              strerror(errno));
     return -1;
   }
@@ -456,8 +456,15 @@ microdesc_cache_rebuild(microdesc_cache_t *cache, int force)
 
     size = dump_microdescriptor(fd, md, &annotation_len);
     if (size < 0) {
-      /* XXX handle errors from dump_microdescriptor() */
-      /* log?  return -1?  die?  coredump the universe? */
+      if (md->saved_location != SAVED_IN_CACHE)
+        tor_free(md->body);
+      md->saved_location = SAVED_NOWHERE;
+      md->off = 0;
+      md->bodylen = 0;
+      md->no_save = 1;
+
+      /* rewind, in case it was a partial write. */
+      tor_fd_setpos(fd, off);
       continue;
     }
     tor_assert(((size_t)size) == annotation_len + md->bodylen);