diff --git a/geometry.go b/geometry.go
index 393f0e8..92ad60d 100644
--- a/geometry.go
+++ b/geometry.go
@@ -6,8 +6,8 @@ import (
 
 // A and B represent two opposite corners of axis-aligned boundin box
 type AABB2d struct {
-	A Point2d `json:A`
-	B Point2d `json:B`
+	A Point2d `json:"A"`
+	B Point2d `json:"B"`
 }
 
 type Polygon2d struct {