diff --git a/Number_types/test/Number_types/Quotient.cpp b/Number_types/test/Number_types/Quotient.cpp
index 267589df53a..e461f00d214 100644
--- a/Number_types/test/Number_types/Quotient.cpp
+++ b/Number_types/test/Number_types/Quotient.cpp
@@ -15,6 +15,8 @@
 #  include <CGAL/leda_integer.h>
 #endif
 
+// template class CGAL::Quotient<CGAL::Gmpz>;
+
 template < typename T >
 void test_double_ctor()
 {
@@ -26,6 +28,13 @@ void test_double_ctor()
   assert(q1.numerator() == T(d1));
   assert(q2.numerator() == 1);
   assert(q2.denominator() == 2);
+
+  // though not exact, implicit operations +,-,* with double 
+  // should be the exactly the same as via explicit ctor! 
+  assert( (q1+0.3) == (q1+Qt(0.3)));
+  assert( (q1-0.3) == (q1-Qt(0.3)));
+  assert( (q1*0.3) == (q1*Qt(0.3)));
+  assert( (q1/0.3) == (q1/Qt(0.3)));
 }
 
 void test_comparison_operators()