diff --git a/selfdrive/common/util.c b/selfdrive/common/util.c
index 9bdb23f99..1aed0eaae 100644
--- a/selfdrive/common/util.c
+++ b/selfdrive/common/util.c
@@ -19,7 +19,9 @@ void* read_file(const char* path, size_t* out_len) {
   long f_len = ftell(f);
   rewind(f);
 
-  char* buf = (char*)calloc(f_len, 1);
+  // calloc one extra byte so the file will always be NULL terminated
+  // cl_cached_program_from_file relies on this
+  char* buf = (char*)calloc(f_len+1, 1);
   assert(buf);
 
   size_t num_read = fread(buf, f_len, 1, f);