diff --git a/mypyc/lib-rt/librt_strings.h b/mypyc/lib-rt/librt_strings.h
index 4069b70ceb439..069bec84a3112 100644
--- a/mypyc/lib-rt/librt_strings.h
+++ b/mypyc/lib-rt/librt_strings.h
@@ -31,7 +31,7 @@ import_librt_strings(void)
 static void *LibRTStrings_API[LIBRT_STRINGS_API_LEN];
 
 // Length of the default buffer embedded directly in a BytesWriter object
-#define WRITER_EMBEDDED_BUF_LEN 512
+#define WRITER_EMBEDDED_BUF_LEN 256
 
 typedef struct {
     PyObject_HEAD