diff --git a/src/math/lp/dioph_eq.cpp b/src/math/lp/dioph_eq.cpp
index 36a81a9d8..41fffcf46 100644
--- a/src/math/lp/dioph_eq.cpp
+++ b/src/math/lp/dioph_eq.cpp
@@ -698,7 +698,9 @@ namespace lp {
                 m_l_matrix.multiply_row(ei, denom);
                 m_e_matrix.multiply_row(ei, denom);
             }
-            
+            if (belongs_to_s(ei)) {
+                remove_from_S(ei);
+            }
             SASSERT(entry_invariant(ei));
         }