diff --git a/cpp/SymbolicConditional.h b/cpp/SymbolicConditional.h
index e07ff4dad..2c4f35f63 100644
--- a/cpp/SymbolicConditional.h
+++ b/cpp/SymbolicConditional.h
@@ -70,7 +70,7 @@ namespace gtsam {
 		}
 
 		/** return any parent */
-		std::list<std::string> parents() { return parents_;}
+		std::list<std::string> parents() const { return parents_;}
 
 	};