diff --git a/changes/bug3135 b/changes/bug3135
new file mode 100644
index 0000000000..d761123480
--- /dev/null
+++ b/changes/bug3135
@@ -0,0 +1,6 @@
+  o Minor bugfixes
+    - Do not crash when our configuration file becomes unreadable
+      (usually due to a permissions change) between when we start
+      up and when a controller calls SAVECONF.  Fixes bug 3135;
+      bugfix on 0.0.9pre6.
+
diff --git a/src/or/config.c b/src/or/config.c
index 5b251d382a..d17ed2462c 100644
--- a/src/or/config.c
+++ b/src/or/config.c
@@ -4764,7 +4764,7 @@ write_configuration_file(const char *fname, or_options_t *options)
   switch (file_status(fname)) {
     case FN_FILE:
       old_val = read_file_to_str(fname, 0, NULL);
-      if (strcmpstart(old_val, GENERATED_FILE_PREFIX)) {
+      if (!old_val || strcmpstart(old_val, GENERATED_FILE_PREFIX)) {
         rename_old = 1;
       }
       tor_free(old_val);