diff --git a/src/orange/surf/GeneralQuadric.hh b/src/orange/surf/GeneralQuadric.hh
index d5408fa38e..eea2be2e0e 100644
--- a/src/orange/surf/GeneralQuadric.hh
+++ b/src/orange/surf/GeneralQuadric.hh
@@ -116,6 +116,8 @@ class GeneralQuadric
 //---------------------------------------------------------------------------//
 /*!
  * Construct with all coefficients.
+ *
+ * TODO: normalize?
  */
 CELER_FUNCTION GeneralQuadric::GeneralQuadric(Real3 const& abc,
                                               Real3 const& def,
@@ -132,6 +134,8 @@ CELER_FUNCTION GeneralQuadric::GeneralQuadric(Real3 const& abc,
     , i_(ghi[2])
     , j_(j)
 {
+    CELER_EXPECT(a_ != 0 || b_ != 0 || c_ != 0 || d_ != 0 || e_ != 0 || f_ != 0
+                 || g_ != 0 || h_ != 0 || i_ != 0);
 }
 
 //---------------------------------------------------------------------------//
diff --git a/src/orange/surf/SimpleQuadric.hh b/src/orange/surf/SimpleQuadric.hh
index 6ff6409c56..bd6852604d 100644
--- a/src/orange/surf/SimpleQuadric.hh
+++ b/src/orange/surf/SimpleQuadric.hh
@@ -123,6 +123,8 @@ class SimpleQuadric
  * Construct with coefficients.
  *
  * The quadric is ill-defined if all non-constants are zero.
+ *
+ * TODO: normalize?
  */
 CELER_FUNCTION
 SimpleQuadric::SimpleQuadric(Real3 const& abc, Real3 const& def, real_type g)