--- a/liboctave/base-qr.cc
+++ b/liboctave/base-qr.cc
@@ -54,3 +54,19 @@
   return retval;
 }
 
+template <class qr_type>
+bool
+base_qr<qr_type>::regular (void) const
+{
+  octave_idx_type k = std::min (r.rows (), r.columns ());
+  bool retval = true;
+  for (octave_idx_type i = 0; i < k; i++)
+    if (r(i, i) == qr_elt_type ())
+      {
+        retval = false;
+        break;
+      }
+
+  return true;
+}
+