diff --git a/src/Function1D.cpp b/src/Function1D.cpp
index c62c573..d2df1b0 100644
--- a/src/Function1D.cpp
+++ b/src/Function1D.cpp
@@ -568,7 +568,9 @@ Matrix Aurora::acosd(const Matrix& aMatrix)
     {
         resultData[i] = resultData[i] * 180 / PI;
     }
-    return Matrix::New(resultData, aMatrix);
+    Matrix result = Matrix::New(resultData, aMatrix);
+    nantoval(result, 0);
+    return result;
 }
 
 Matrix Aurora::conj(const Matrix& aMatrix)