diff --git a/toonz/sources/common/tcore/tmathutil.cpp b/toonz/sources/common/tcore/tmathutil.cpp
index 4f15e6b..bf6e807 100644
--- a/toonz/sources/common/tcore/tmathutil.cpp
+++ b/toonz/sources/common/tcore/tmathutil.cpp
@@ -44,7 +44,7 @@ inline int getEl(int i, int j, int n)
 typedef struct
 	{
 	int ord;
-	double coef[MAX_ORDER];
+	double coef[MAX_ORDER + 1];
 } poly;
 
 //-------------------------------------------------------------------------