diff --git a/obudec.c b/obudec.c
index 855de96..abcf065 100644
--- a/obudec.c
+++ b/obudec.c
@@ -103,7 +103,7 @@
     }
 
     data = *buffer + (*buffer_size);
-    *buffer_size += obu_size;
+    *buffer_size += (size_t)obu_size;
     ret = fread(data, 1, (size_t)obu_size, infile);
 
     if (ret != obu_size) {