diff --git a/libc/system_properties/contexts_split.cpp b/libc/system_properties/contexts_split.cpp
index 92baedd..11db7ec 100644
--- a/libc/system_properties/contexts_split.cpp
+++ b/libc/system_properties/contexts_split.cpp
@@ -196,7 +196,7 @@
 bool ContextsSplit::MapSerialPropertyArea(bool access_rw, bool* fsetxattr_failed) {
   char filename[PROP_FILENAME_MAX];
   int len = async_safe_format_buffer(filename, sizeof(filename), "%s/properties_serial", filename_);
-  if (len < 0 || len > PROP_FILENAME_MAX) {
+  if (len < 0 || len >= PROP_FILENAME_MAX) {
     serial_prop_area_ = nullptr;
     return false;
   }