diff --git a/src/Numerics/LinearAlgebra/Double/Matrix.cs b/src/Numerics/LinearAlgebra/Double/Matrix.cs
index 0eec7f0b..bf46f7f3 100644
--- a/src/Numerics/LinearAlgebra/Double/Matrix.cs
+++ b/src/Numerics/LinearAlgebra/Double/Matrix.cs
@@ -99,7 +99,7 @@ namespace MathNet.Numerics.LinearAlgebra.Double
             var norm = 0.0;
             for (var i = 0; i < RowCount; i++)
             {
-                norm += Math.Abs(aat.At(i, i));
+                norm += aat.At(i, i);
             }
 
             norm = Math.Sqrt(norm);
diff --git a/src/Numerics/LinearAlgebra/Single/Matrix.cs b/src/Numerics/LinearAlgebra/Single/Matrix.cs
index e33088b9..685fe010 100644
--- a/src/Numerics/LinearAlgebra/Single/Matrix.cs
+++ b/src/Numerics/LinearAlgebra/Single/Matrix.cs
@@ -99,7 +99,7 @@ namespace MathNet.Numerics.LinearAlgebra.Single
             var norm = 0.0f;
             for (var i = 0; i < RowCount; i++)
             {
-                norm += Math.Abs(aat.At(i, i));
+                norm += aat.At(i, i);
             }
 
             norm = Convert.ToSingle(Math.Sqrt(norm));