diff --git a/src/Function2D.cpp b/src/Function2D.cpp
index aa78bf9..a42570e 100644
--- a/src/Function2D.cpp
+++ b/src/Function2D.cpp
@@ -345,7 +345,7 @@ Matrix Aurora::sum(const Matrix &aMatrix, FunctionDirection direction) {
             {
                 Eigen::Map<Eigen::MatrixXd> srcM(aMatrix.getData(),aMatrix.getDimSize(0),aMatrix.getDimSize(1));
                 double * ret = malloc(aMatrix.getDimSize(1));
-                Eigen::Map<Eigen::VectorXd> retV(ret,aMatrix.getDimSize(0));
+                Eigen::Map<Eigen::VectorXd> retV(ret,aMatrix.getDimSize(1));
                 retV = srcM.colwise().sum();
                 return Matrix::New(ret,1,aMatrix.getDimSize(1));
             }