diff --git a/webmin/webmin-lib.pl b/webmin/webmin-lib.pl
index 1fdcdb799..30447b3dd 100755
--- a/webmin/webmin-lib.pl
+++ b/webmin/webmin-lib.pl
@@ -1618,7 +1618,7 @@ sub prefix_to_mask
 {
 return $_[0] >= 24 ? "255.255.255.".(256-(2 ** (32-$_[0]))) :
        $_[0] >= 16 ? "255.255.".(256-(2 ** (24-$_[0]))).".0" :
-       $_[0] >= 16 ? "255.".(256-(2 ** (16-$_[0]))).".0.0" :
+       $_[0] >= 8 ? "255.".(256-(2 ** (16-$_[0]))).".0.0" :
                      (256-(2 ** (8-$_[0]))).".0.0.0";
 }