diff --git a/Numeric/fullMatrix.h b/Numeric/fullMatrix.h
index e76184055e127ca489ccbd15cf36ce5dce0d8fa9..d9256611b905da6b3004865d583dd799484da266 100644
--- a/Numeric/fullMatrix.h
+++ b/Numeric/fullMatrix.h
@@ -501,7 +501,7 @@ class fullMatrix
     if (nbRows != -1 && nbColumns == -1)
       nbColumns = _r * _c / nbRows;
     if (nbRows*nbColumns != size1()*size2())
-      Msg::Error("Invalid reshape, total number of entries must be equal");
+      Msg::Error("Invalid reshape, total number of entries must be equal (new %i x %i != old %i x %i)", nbRows, nbColumns, size1(), size2());
     _r = nbRows;
     _c = nbColumns;
   }