diff --git a/codegen/Cargo.toml b/codegen/Cargo.toml
index 212801e..09be5de 100644
--- a/codegen/Cargo.toml
+++ b/codegen/Cargo.toml
@@ -10,4 +10,4 @@
 [dependencies]
 syn = { version = "1.0.6", features = ["full", "extra-traits"] }
 quote = "1.0.2"
-proc-macro2 = "1.0.6"
+proc-macro2 = "=1.0.43"