diff --git a/src/flags.rs b/src/flags.rs
index 0aed8c5..cf55ce4 100644
--- a/src/flags.rs
+++ b/src/flags.rs
@@ -91,7 +91,7 @@ static DEFAULT_RUSTFLAGS: &[&[&str]] = &[
         "-Zmaximal-hir-to-mir-coverage",
         "-Zstrict-init-checks=yes",
         "-Zcrate-attr=feature(explicit_tail_calls)",
-        //        "-Zcrate-attr=feature(effects)",
+        "-Zcrate-attr=feature(effects)",
         //  "-Clto=off", // rustc_codegen_gcc
         //   "-Ztreat-err-as-bug=3",
         "-Zcrate-attr=feature(lazy_type_alias)",
@@ -136,7 +136,7 @@ static DEFAULT_RUSTFLAGS: &[&[&str]] = &[
         "-Zcrate-attr=feature(explicit_tail_calls)",
         "-Zcrate-attr=feature(lazy_type_alias)",
         "-Zcrate-attr=feature(generic_const_items)",
-        //     "-Zcrate-attr=feature(effects)",
+        "-Zcrate-attr=feature(effects)",
         // "-Clto=off", // rustc_codegen_gcc
         //    "-Ztreat-err-as-bug=3",
         "-Ztrait-solver=next-coherence",
@@ -190,7 +190,7 @@ static DEFAULT_RUSTFLAGS: &[&[&str]] = &[
         "-Zcrate-attr=feature(explicit_tail_calls)",
         "-Zcrate-attr=feature(lazy_type_alias)",
         "-Zcrate-attr=feature(impl_trait_projections)",
-        // "-Zcrate-attr=feature(effects)",
+        "-Zcrate-attr=feature(effects)",
         // "-Clto=off", // rustc_codegen_gcc
         //   "-Ztreat-err-as-bug=3",
         "-Ztrait-solver=next-coherence",