diff --git a/dlls/d3dxof/parsing.c b/dlls/d3dxof/parsing.c
index f40c202e82..9f426c46b5 100644
--- a/dlls/d3dxof/parsing.c
+++ b/dlls/d3dxof/parsing.c
@@ -605,7 +605,7 @@ static BOOL is_string(parse_buffer* buf)
   if (*buf->buffer != '"')
     return FALSE;
 
-  while (pos < buf->rem_bytes && !is_operator(c = *(buf->buffer+pos+1)))
+  while ((pos+1) < buf->rem_bytes && !is_operator(c = *(buf->buffer+pos+1)))
   {
     if (c == '"')
     {