diff --git a/src/library/blast/blast.cpp b/src/library/blast/blast.cpp
index 4511b00b2..203606574 100644
--- a/src/library/blast/blast.cpp
+++ b/src/library/blast/blast.cpp
@@ -105,6 +105,17 @@ class blastenv {
     unfold_macro_pred          m_unfold_macro_pred;
     bool                       m_classical{false};
 
+    bool is_extra_opaque(name const & n) const {
+        // TODO(Leo, Daniel): should we force 'not' to be always opaque?
+        // If we do that, we can remove the whnf-trick from unit_propagate.
+        // We can also avoid the `is_pi(type) && !is_prop(type)`
+        if (n == get_ne_name())
+            return false;
+        return
+            (m_not_reducible_pred(n) ||
+             m_projection_info.contains(n));
+    }
+
     class tctx : public type_context {
         blastenv &                              m_benv;
         std::vector<state::assignment_snapshot> m_stack;
@@ -114,8 +125,7 @@ class blastenv {
             m_benv(benv) {}
 
         virtual bool is_extra_opaque(name const & n) const override {
-            // TODO(Leo): class and instances
-            return m_benv.m_not_reducible_pred(n) || m_benv.m_projection_info.contains(n);
+            return m_benv.is_extra_opaque(n);
         }
 
         virtual bool should_unfold_macro(expr const & e) const override {
diff --git a/src/library/constants.cpp b/src/library/constants.cpp
index ef28bb6b8..3cdddf03b 100644
--- a/src/library/constants.cpp
+++ b/src/library/constants.cpp
@@ -80,6 +80,7 @@ name const * g_nat = nullptr;
 name const * g_nat_of_num = nullptr;
 name const * g_nat_succ = nullptr;
 name const * g_nat_zero = nullptr;
+name const * g_ne = nullptr;
 name const * g_neg = nullptr;
 name const * g_not = nullptr;
 name const * g_not_of_iff_false = nullptr;
@@ -265,6 +266,7 @@ void initialize_constants() {
     g_nat_of_num = new name{"nat", "of_num"};
     g_nat_succ = new name{"nat", "succ"};
     g_nat_zero = new name{"nat", "zero"};
+    g_ne = new name{"ne"};
     g_neg = new name{"neg"};
     g_not = new name{"not"};
     g_not_of_iff_false = new name{"not_of_iff_false"};
@@ -451,6 +453,7 @@ void finalize_constants() {
     delete g_nat_of_num;
     delete g_nat_succ;
     delete g_nat_zero;
+    delete g_ne;
     delete g_neg;
     delete g_not;
     delete g_not_of_iff_false;
@@ -636,6 +639,7 @@ name const & get_nat_name() { return *g_nat; }
 name const & get_nat_of_num_name() { return *g_nat_of_num; }
 name const & get_nat_succ_name() { return *g_nat_succ; }
 name const & get_nat_zero_name() { return *g_nat_zero; }
+name const & get_ne_name() { return *g_ne; }
 name const & get_neg_name() { return *g_neg; }
 name const & get_not_name() { return *g_not; }
 name const & get_not_of_iff_false_name() { return *g_not_of_iff_false; }
diff --git a/src/library/constants.h b/src/library/constants.h
index 7a68b2bff..d60a93531 100644
--- a/src/library/constants.h
+++ b/src/library/constants.h
@@ -82,6 +82,7 @@ name const & get_nat_name();
 name const & get_nat_of_num_name();
 name const & get_nat_succ_name();
 name const & get_nat_zero_name();
+name const & get_ne_name();
 name const & get_neg_name();
 name const & get_not_name();
 name const & get_not_of_iff_false_name();
diff --git a/src/library/constants.txt b/src/library/constants.txt
index 9177f7d1b..fc23fdf56 100644
--- a/src/library/constants.txt
+++ b/src/library/constants.txt
@@ -75,6 +75,7 @@ nat
 nat.of_num
 nat.succ
 nat.zero
+ne
 neg
 not
 not_of_iff_false
diff --git a/tests/lean/run/blast_cc12.lean b/tests/lean/run/blast_cc12.lean
index 2dba59441..781d76a0a 100644
--- a/tests/lean/run/blast_cc12.lean
+++ b/tests/lean/run/blast_cc12.lean
@@ -22,4 +22,9 @@ attribute not [reducible]
 definition foo4 (a b c d : nat) (p : Prop) : a ≠ d → (d ≠ a → p) → p :=
 by blast
 
-print foo4
+attribute ne [semireducible]
+
+definition foo5 (a b c d : nat) (p : Prop) : a ≠ d → (d ≠ a → p) → p :=
+by blast
+
+print foo5