diff --git a/src/math/lp/stacked_vector.h b/src/math/lp/stacked_vector.h
index 61131955ada..ecd61eb10fb 100644
--- a/src/math/lp/stacked_vector.h
+++ b/src/math/lp/stacked_vector.h
@@ -55,6 +55,9 @@ template < typename B> class stacked_vector {
         bool operator==(B const& other) const {
             return m_vec.m_vector[m_i] == other;
         }
+        bool operator!=(B const& other) const {
+            return m_vec.m_vector[m_i] != other;
+        }
         B& operator+=(B const &delta) {
             // not tracking the change here!
             return m_vec.m_vector[m_i] += delta;