Index: b/Cargo.toml
===================================================================
--- a/Cargo.toml
+++ b/Cargo.toml
@@ -46,7 +46,7 @@
 path = "src/lib.rs"
 
 [dependencies.heck]
-version = "0.5"
+version = ">= 0.4, < 0.6"
 
 [dependencies.proc-macro2]
 version = "1.0.60"
