diff --git a/quickcheck_macros/Cargo.toml b/quickcheck_macros/Cargo.toml
index 1d9041d..d05db15 100644
--- a/quickcheck_macros/Cargo.toml
+++ b/quickcheck_macros/Cargo.toml
@@ -19,7 +19,7 @@ proc-macro = true
 [dependencies]
 proc-macro2 = "1.0"
 quote = "1.0"
-syn = { version = "1.0", features = ["full"] }
+syn = { version = "2.0", features = ["full"] }
 
 [dev-dependencies]
 quickcheck = { path = "..", version = "1.0.0" }
diff --git a/quickcheck_macros/src/lib.rs b/quickcheck_macros/src/lib.rs
index 132e8e0..25eb3fa 100644
--- a/quickcheck_macros/src/lib.rs
+++ b/quickcheck_macros/src/lib.rs
@@ -33,6 +33,13 @@ pub fn quickcheck(_args: TokenStream, input: TokenStream) -> TokenStream {
             if errors.is_empty() {
                 let attrs = mem::replace(&mut item_fn.attrs, Vec::new());
                 let name = &item_fn.sig.ident;
+                if let Some(variadic) = &item_fn.sig.variadic {
+                    // variadics are just for `extern fn`
+                    errors.push(syn::parse::Error::new(
+                        variadic.span(),
+                        "unsupported variadic",
+                    ));
+                }
                 let fn_type = syn::TypeBareFn {
                     lifetimes: None,
                     unsafety: item_fn.sig.unsafety.clone(),
@@ -40,7 +47,7 @@ pub fn quickcheck(_args: TokenStream, input: TokenStream) -> TokenStream {
                     fn_token: <syn::Token![fn]>::default(),
                     paren_token: syn::token::Paren::default(),
                     inputs,
-                    variadic: item_fn.sig.variadic.clone(),
+                    variadic: None,
                     output: item_fn.sig.output.clone(),
                 };