diff --git a/lib/Cargo.toml b/lib/Cargo.toml
index a2ae4253..91d169d0 100644
--- a/lib/Cargo.toml
+++ b/lib/Cargo.toml
@@ -180,7 +180,7 @@ time-module = []
 
 # Features that are enabled by default.
 default = [
-    #"constant-folding",
+    "constant-folding",
     "cuckoo-module",
     "exact-atoms",
     "fast-regexp",