diff --git a/src/contrib/newmat/newmat6.cpp b/src/contrib/newmat/newmat6.cpp
index ef89b430..3bb3fb31 100644
--- a/src/contrib/newmat/newmat6.cpp
+++ b/src/contrib/newmat/newmat6.cpp
@@ -428,7 +428,7 @@ void CroutMatrix::operator=(const CroutMatrix& gm)
 {
    if (&gm == this) { REPORT tag_val = -1; return; }
    REPORT
-   if (indx > 0) { delete [] indx; indx = 0; }
+   if (indx != NULL) { delete [] indx; indx = 0; }
    ((CroutMatrix&)gm).get_aux(*this);
    Eq(gm);
 }