diff --git a/sourceCode/BQ_workpieceCornerExtraction.cpp b/sourceCode/BQ_workpieceCornerExtraction.cpp
index 6aebc31..5aaa912 100644
--- a/sourceCode/BQ_workpieceCornerExtraction.cpp
+++ b/sourceCode/BQ_workpieceCornerExtraction.cpp
@@ -410,8 +410,18 @@ SSX_BQworkpieceResult sx_BQ_getWorkpieceCorners(
 	SVzNL3DPoint firstPt = region[0].edge[0];
 	SVzNL3DPoint lastPt = region[0].edge.back();
 	int idx0 = _getPointClosestContour(v_trees, true, firstPt, scanLines, true);
+	if (idx0 < 0)
+	{
+		*errCode = SX_ERR_INVLD_CLOSES_PT;
+		return;
+	}
 	_getEdgeLinkingContour(&v_trees[idx0], true, firstPt, region[0].edgeLink_1, scanLines, true, workpieceParam.lineLen);
 	int idx1 = _getPointClosestContour(v_trees, true, lastPt, scanLines, true);
+	if (idx1 < 0)
+	{
+		*errCode = SX_ERR_INVLD_CLOSES_PT;
+		return;
+	}
 	_getEdgeLinkingContour(&v_trees[idx1], true, lastPt, region[0].edgeLink_2, scanLines, true, workpieceParam.lineLen);
 	if ((region[0].edgeLink_1.size() < 5) || (region[0].edgeLink_2.size() < 5))
 	{
@@ -425,8 +435,18 @@ SSX_BQworkpieceResult sx_BQ_getWorkpieceCorners(
 	firstPt = region[1].edge[0];
 	lastPt = region[1].edge.back();
 	idx0 = _getPointClosestContour(h_trees, false, firstPt, scanLines, true);
+	if (idx0 < 0)
+	{
+		*errCode = SX_ERR_INVLD_CLOSES_PT;
+		return;
+	}
 	_getEdgeLinkingContour(&h_trees[idx0], false, firstPt, region[1].edgeLink_1, scanLines, true, workpieceParam.lineLen);
 	idx1 = _getPointClosestContour(h_trees, false, lastPt, scanLines, true);
+	if (idx1 < 0)
+	{
+		*errCode = SX_ERR_INVLD_CLOSES_PT;
+		return;
+	}
 	_getEdgeLinkingContour(&h_trees[idx1], false, lastPt, region[1].edgeLink_2, scanLines, true, workpieceParam.lineLen);
 	if ((region[1].edgeLink_1.size() < 5) || (region[1].edgeLink_2.size() < 5))
 	{
@@ -439,8 +459,18 @@ SSX_BQworkpieceResult sx_BQ_getWorkpieceCorners(
 	firstPt = region[2].edge[0];
 	lastPt = region[2].edge.back();
 	idx0 = _getPointClosestContour(v_trees, true, firstPt, scanLines, false);
+	if (idx0 < 0)
+	{
+		*errCode = SX_ERR_INVLD_CLOSES_PT;
+		return;
+	}
 	_getEdgeLinkingContour(&v_trees[idx0], true, firstPt, region[2].edgeLink_1, scanLines, false, workpieceParam.lineLen);
 	idx1 = _getPointClosestContour(v_trees, true, lastPt, scanLines, false);
+	if (idx1 < 0)
+	{
+		*errCode = SX_ERR_INVLD_CLOSES_PT;
+		return;
+	}
 	_getEdgeLinkingContour(&v_trees[idx1], true, lastPt, region[2].edgeLink_2, scanLines, false, workpieceParam.lineLen);
 	if ((region[2].edgeLink_1.size() < 5) || (region[2].edgeLink_2.size() < 5))
 	{
@@ -453,8 +483,18 @@ SSX_BQworkpieceResult sx_BQ_getWorkpieceCorners(
 	firstPt = region[3].edge[0];
 	lastPt = region[3].edge.back();
 	idx0 = _getPointClosestContour(h_trees, false, firstPt, scanLines, true);
+	if (idx0 < 0)
+	{
+		*errCode = SX_ERR_INVLD_CLOSES_PT;
+		return;
+	}
 	_getEdgeLinkingContour(&h_trees[idx0], false, firstPt, region[3].edgeLink_1, scanLines, false, workpieceParam.lineLen);
 	idx1 = _getPointClosestContour(h_trees, false, lastPt, scanLines, true);
+	if (idx1 < 0)
+	{
+		*errCode = SX_ERR_INVLD_CLOSES_PT;
+		return;
+	}
 	_getEdgeLinkingContour(&h_trees[idx1], false, lastPt, region[3].edgeLink_2, scanLines, false, workpieceParam.lineLen);
 	if ((region[3].edgeLink_1.size() < 5) || (region[3].edgeLink_2.size() < 5))
 	{
diff --git a/sourceCode/SG_errCode.h b/sourceCode/SG_errCode.h
index e61d36e..a35b02a 100644
--- a/sourceCode/SG_errCode.h
+++ b/sourceCode/SG_errCode.h
@@ -10,4 +10,5 @@
 //BQ_workpiece
 #define SX_ERR_INVLD_VTREE_NUM		-2001
 #define SX_ERR_INVLD_HTREE_NUM		-2002
-#define SX_ERR_INVLD_EDGE_LINK_NUM	-2003
\ No newline at end of file
+#define SX_ERR_INVLD_EDGE_LINK_NUM	-2003
+#define SX_ERR_INVLD_CLOSES_PT		-2004
\ No newline at end of file