diff --git a/src/library/blast/recursor_action.cpp b/src/library/blast/recursor_action.cpp
index 385a0a7e7..c943c682f 100644
--- a/src/library/blast/recursor_action.cpp
+++ b/src/library/blast/recursor_action.cpp
@@ -20,8 +20,6 @@ struct recursor_branch_extension : public branch_extension {
     recursor_branch_extension(recursor_branch_extension const & b):m_rec_queue(b.m_rec_queue) {}
     virtual ~recursor_branch_extension() {}
     virtual branch_extension * clone() { return new recursor_branch_extension(*this); }
-    virtual void hypothesis_activated(hypothesis const &, hypothesis_idx) {}
-    virtual void hypothesis_deleted(hypothesis const &, hypothesis_idx) {}
 };
 
 void initialize_recursor_action() {
diff --git a/src/library/blast/state.cpp b/src/library/blast/state.cpp
index 672d35a6f..af45c44ae 100644
--- a/src/library/blast/state.cpp
+++ b/src/library/blast/state.cpp
@@ -712,6 +712,7 @@ branch_extension & state::get_extension(unsigned extid) {
         ext->inc_ref();
         m_branch.m_extensions[extid] = ext;
         lean_assert(ext.get_rc() == 1);
+        ext->initialized();
         m_branch.m_active.for_each([&](hypothesis_idx hidx) {
                 hypothesis const * h = get_hypothesis_decl(hidx);
                 lean_assert(h);
diff --git a/src/library/blast/state.h b/src/library/blast/state.h
index 8bae1a751..7811260fc 100644
--- a/src/library/blast/state.h
+++ b/src/library/blast/state.h
@@ -104,8 +104,9 @@ class branch_extension {
 public:
     virtual ~branch_extension() {}
     virtual branch_extension * clone() = 0;
-    virtual void hypothesis_activated(hypothesis const & h, hypothesis_idx hidx) = 0;
-    virtual void hypothesis_deleted(hypothesis const & h, hypothesis_idx hidx) = 0;
+    virtual void initialized() {}
+    virtual void hypothesis_activated(hypothesis const &, hypothesis_idx) {}
+    virtual void hypothesis_deleted(hypothesis const &, hypothesis_idx) {}
 };
 
 unsigned register_branch_extension(branch_extension * initial);