diff --git a/src/goto-symex/symex_target_equation.h b/src/goto-symex/symex_target_equation.h
index bada3f9d871..0462bdb8bd4 100644
--- a/src/goto-symex/symex_target_equation.h
+++ b/src/goto-symex/symex_target_equation.h
@@ -320,7 +320,7 @@ class symex_target_equationt:public symex_targett
 
 protected:
   // for enforcing sharing in the expressions stored
-  merge_irept merge_irep;
+  merge_full_irept merge_irep;
   void merge_ireps(SSA_stept &SSA_step);
 };