diff --git a/vpx_dsp/prob.h b/vpx_dsp/prob.h
index 148116ed08994e5c0db84cd47f7a8acc51ea0077..6b4f7f9e2071e3b3b344619e9041165b6d433fea 100644
--- a/vpx_dsp/prob.h
+++ b/vpx_dsp/prob.h
@@ -28,7 +28,7 @@ typedef uint8_t vpx_prob;
 
 typedef int8_t vpx_tree_index;
 
-#define TREE_SIZE(leaf_count) (2 * (leaf_count)-2)
+#define TREE_SIZE(leaf_count) (-2 + 2 * (leaf_count))
 
 #define vpx_complement(x) (255 - x)