diff --git a/src/library/constants.cpp b/src/library/constants.cpp
index 1dcdfe3dd3..36b9a2a8b7 100644
--- a/src/library/constants.cpp
+++ b/src/library/constants.cpp
@@ -179,6 +179,7 @@ name const * g_is_trunc_is_prop_elim = nullptr;
 name const * g_is_trunc_is_set = nullptr;
 name const * g_ite = nullptr;
 name const * g_left_distrib = nullptr;
+name const * g_left_comm = nullptr;
 name const * g_le = nullptr;
 name const * g_le_refl = nullptr;
 name const * g_lift = nullptr;
@@ -631,6 +632,7 @@ void initialize_constants() {
     g_is_trunc_is_set = new name{"is_trunc", "is_set"};
     g_ite = new name{"ite"};
     g_left_distrib = new name{"left_distrib"};
+    g_left_comm = new name{"left_comm"};
     g_le = new name{"le"};
     g_le_refl = new name{"le", "refl"};
     g_lift = new name{"lift"};
@@ -1084,6 +1086,7 @@ void finalize_constants() {
     delete g_is_trunc_is_set;
     delete g_ite;
     delete g_left_distrib;
+    delete g_left_comm;
     delete g_le;
     delete g_le_refl;
     delete g_lift;
@@ -1536,6 +1539,7 @@ name const & get_is_trunc_is_prop_elim_name() { return *g_is_trunc_is_prop_elim;
 name const & get_is_trunc_is_set_name() { return *g_is_trunc_is_set; }
 name const & get_ite_name() { return *g_ite; }
 name const & get_left_distrib_name() { return *g_left_distrib; }
+name const & get_left_comm_name() { return *g_left_comm; }
 name const & get_le_name() { return *g_le; }
 name const & get_le_refl_name() { return *g_le_refl; }
 name const & get_lift_name() { return *g_lift; }
diff --git a/src/library/constants.h b/src/library/constants.h
index f1b843fd60..6d93d86078 100644
--- a/src/library/constants.h
+++ b/src/library/constants.h
@@ -181,6 +181,7 @@ name const & get_is_trunc_is_prop_elim_name();
 name const & get_is_trunc_is_set_name();
 name const & get_ite_name();
 name const & get_left_distrib_name();
+name const & get_left_comm_name();
 name const & get_le_name();
 name const & get_le_refl_name();
 name const & get_lift_name();
diff --git a/src/library/constants.txt b/src/library/constants.txt
index 8b96ac1223..6b9159a2f3 100644
--- a/src/library/constants.txt
+++ b/src/library/constants.txt
@@ -174,6 +174,7 @@ is_trunc.is_prop.elim
 is_trunc.is_set
 ite
 left_distrib
+left_comm
 le
 le.refl
 lift
diff --git a/src/library/tactic/ac_tactics.cpp b/src/library/tactic/ac_tactics.cpp
index 58dea32ff5..f331372957 100644
--- a/src/library/tactic/ac_tactics.cpp
+++ b/src/library/tactic/ac_tactics.cpp
@@ -248,7 +248,7 @@ struct perm_ac_fn : public flat_assoc_fn {
         if (!m_left_comm) {
             expr A    = m_ctx.infer(a);
             level lvl = get_level(m_ctx, A);
-            m_left_comm = mk_app(mk_constant(name{"binary", "left_comm"}, {lvl}), A, m_op, m_comm, m_assoc);
+            m_left_comm = mk_app(mk_constant(get_left_comm_name(), {lvl}), A, m_op, m_comm, m_assoc);
         }
         return mk_app(*m_left_comm, a, b, c);
     }