diff --git a/lucene/CHANGES.txt b/lucene/CHANGES.txt
index 7de2179817d0..bf74298891eb 100644
--- a/lucene/CHANGES.txt
+++ b/lucene/CHANGES.txt
@@ -80,6 +80,8 @@ Bug Fixes
 
 * GITHUB#12220: Hunspell: disallow hidden title-case entries from compound middle/end
 
+* GITHUB#12287: Fix a bug in ShapeTestUtil. (Heemin Kim)
+
 Other
 ---------------------
 
diff --git a/lucene/test-framework/src/java/org/apache/lucene/tests/geo/ShapeTestUtil.java b/lucene/test-framework/src/java/org/apache/lucene/tests/geo/ShapeTestUtil.java
index e0e8c6964fce..aed0a92ea4ca 100644
--- a/lucene/test-framework/src/java/org/apache/lucene/tests/geo/ShapeTestUtil.java
+++ b/lucene/test-framework/src/java/org/apache/lucene/tests/geo/ShapeTestUtil.java
@@ -99,10 +99,10 @@ private static XYPolygon trianglePolygon(XYRectangle box) {
     final float[] polyY = new float[4];
     polyX[0] = box.minX;
     polyY[0] = box.minY;
-    polyX[1] = box.minX;
+    polyX[1] = box.maxX;
     polyY[1] = box.minY;
-    polyX[2] = box.minX;
-    polyY[2] = box.minY;
+    polyX[2] = box.maxX;
+    polyY[2] = box.maxY;
     polyX[3] = box.minX;
     polyY[3] = box.minY;
     return new XYPolygon(polyX, polyY);
@@ -142,12 +142,12 @@ private static XYPolygon boxPolygon(XYRectangle box) {
     final float[] polyY = new float[5];
     polyX[0] = box.minX;
     polyY[0] = box.minY;
-    polyX[1] = box.minX;
+    polyX[1] = box.maxX;
     polyY[1] = box.minY;
-    polyX[2] = box.minX;
-    polyY[2] = box.minY;
+    polyX[2] = box.maxX;
+    polyY[2] = box.maxY;
     polyX[3] = box.minX;
-    polyY[3] = box.minY;
+    polyY[3] = box.maxY;
     polyX[4] = box.minX;
     polyY[4] = box.minY;
     return new XYPolygon(polyX, polyY);