diff --git a/src/main/scala/leon/synthesis/rules/CEGLESS.scala b/src/main/scala/leon/synthesis/rules/CEGLESS.scala
index e2e8c9fabc04cddea941b5b807a2df89f9742862..c12edac075bc8525d395d5f792ef4579c0d109f1 100644
--- a/src/main/scala/leon/synthesis/rules/CEGLESS.scala
+++ b/src/main/scala/leon/synthesis/rules/CEGLESS.scala
@@ -30,7 +30,7 @@ case object CEGLESS extends CEGISLike[NonTerminal[String]]("CEGLESS") {
       }
     }
 
-    val guidedGrammar = guides.map(SimilarTo(_, inputs.toSet, sctx, p)).foldLeft[ExpressionGrammar[NonTerminal[String]]](Empty())(_ || _)
+    val guidedGrammar = Union(guides.map(SimilarTo(_, inputs.toSet, sctx, p)))
 
     CegisParams(
       grammar = guidedGrammar,