diff --git a/src/main/scala/leon/evaluators/AbstractEvaluator.scala b/src/main/scala/leon/evaluators/AbstractEvaluator.scala
index ae0333ec960b88b0be80149ddcb61b07cc757ad8..a876001683a2592e567b42f68747e4b86d462d20 100644
--- a/src/main/scala/leon/evaluators/AbstractEvaluator.scala
+++ b/src/main/scala/leon/evaluators/AbstractEvaluator.scala
@@ -22,6 +22,7 @@ class AbstractEvaluator(ctx: LeonContext, prog: Program) extends ContextualEvalu
   /** Evaluates resuts which can be evaluated directly
     * For example, concatenation of two string literals */
   val underlying = new DefaultEvaluator(ctx, prog)
+  underlying.setEvaluationFailOnChoose(true)
   override type Value = (Expr, Expr)
 
   override val description: String = "Evaluates string programs but keeps the formula which generated the string"