diff --git a/src/muz/pdr/pdr_farkas_learner.cpp b/src/muz/pdr/pdr_farkas_learner.cpp
index b440ef519..7c38bf86f 100644
--- a/src/muz/pdr/pdr_farkas_learner.cpp
+++ b/src/muz/pdr/pdr_farkas_learner.cpp
@@ -905,6 +905,7 @@ namespace pdr {
     void farkas_learner::get_asserted(proof* p, expr_set const& bs, ast_mark& b_closed, obj_hashtable<expr>& lemma_set, expr_ref_vector& lemmas) {
         ast_manager& m = lemmas.get_manager();
         ast_mark visited;
+        proof* p0 = p;
         ptr_vector<proof> todo;        
         todo.push_back(p);