diff --git a/crates/luaffi/src/lib.rs b/crates/luaffi/src/lib.rs
index 07d9ef1..0a632c2 100644
--- a/crates/luaffi/src/lib.rs
+++ b/crates/luaffi/src/lib.rs
@@ -434,7 +434,7 @@ impl<'r, 'm> MetatypeMethodBuilder<'r, 'm> {
         write!(self.prelude, "local __{name}_len = 0; ").unwrap();
         write!(
             self.prelude,
-            r#"if {name} ~= nil then assert(type({name}) == "string", "expected string in argument '{name}', got " .. type({name})); __{name}_len = #{name}; end; "#
+            r#"if {name} ~= nil then assert(type({name}) == "string", "string expected in argument '{name}', got " .. type({name})); __{name}_len = #{name}; end; "#
         )
         .unwrap();
         self
@@ -520,7 +520,7 @@ macro_rules! impl_copy_primitive {
             type FromValue = $rtype;
 
             fn prelude(arg: &str) -> impl Display {
-                display!(r#"assert(type({arg}) == "{0}", "expected {0} in argument '{arg}', got " .. type({arg})); "#, $ltype)
+                display!(r#"assert(type({arg}) == "{0}", "{0} expected in argument '{arg}', got " .. type({arg})); "#, $ltype)
             }
 
             fn convert(from: Self::From) -> Self {
diff --git a/crates/luaffi/src/string.rs b/crates/luaffi/src/string.rs
index 1fef94f..6edfe6b 100644
--- a/crates/luaffi/src/string.rs
+++ b/crates/luaffi/src/string.rs
@@ -24,7 +24,7 @@ unsafe impl FromFfi for *const [u8] {
             let ct = lua_buf::name();
             write!(
                 f,
-                r#"if {arg} ~= nil then assert(type({arg}) == "string", "expected string in argument '{arg}', got " .. type({arg})); "#
+                r#"if {arg} ~= nil then assert(type({arg}) == "string", "string expected in argument '{arg}', got " .. type({arg})); "#
             )?;
             write!(f, "{arg} = {ct}({arg}, #{arg}); end; ")
         })
@@ -55,7 +55,7 @@ unsafe impl FromFfi for &str {
             let ct = lua_buf::name();
             write!(
                 f,
-                r#"assert(type({arg}) == "string", "expected string in argument '{arg}', got " .. type({arg})); "#
+                r#"assert(type({arg}) == "string", "string expected in argument '{arg}', got " .. type({arg})); "#
             )?;
             write!(
                 f,
diff --git a/crates/luaify/src/transform.rs b/crates/luaify/src/transform.rs
index 28dbbf3..43fefcd 100644
--- a/crates/luaify/src/transform.rs
+++ b/crates/luaify/src/transform.rs
@@ -146,14 +146,14 @@ impl Visitor {
         //
         if let Expr::Cast(cast) = expr {
             let arg = (*cast.expr).clone();
-            let mut init: Option<Stmt> = None;
+            let mut prelude: Option<Stmt> = None;
             let ty: LuaType = (&*cast.ty).try_into()?;
             let ty_str = format!("{ty}");
             let (ident, msg) = match unwrap_expr_ident(&arg).ok() {
                 Some(ident) => (ident.clone(), format!("{ty} expected in '{ident}', got ")),
                 None => {
                     let ident = Ident::new("_", arg.span());
-                    init = Some(parse_quote! { let #ident = #arg; });
+                    prelude = Some(parse_quote! { let #ident = #arg; });
                     (ident, format!("{ty} expected, got "))
                 }
             };
@@ -163,40 +163,32 @@ impl Visitor {
             *expr = match ty {
                 LuaType::Any => parse_quote_spanned!(span => {}),
                 LuaType::Nil => parse_quote_spanned!(span => {
-                    #init
-                    if #ident != () {
-                        return error(concat!(#msg, r#type(#ident)));
-                    }
+                    #prelude
+                    assert(#ident == (), concat!(#msg, r#type(#ident)));
                 }),
                 LuaType::Number => parse_quote_spanned!(span => {
-                    #init
+                    #prelude
                     let #tmp = #ident;
                     #ident = tonumber(#ident);
-                    if #ident == () {
-                        return error(concat!(#msg, r#type(#tmp)));
-                    }
+                    assert(#ident != (), concat!(#msg, r#type(#tmp)));
                 }),
                 LuaType::Integer => parse_quote_spanned!(span => {
-                    #init
+                    #prelude
                     let #tmp = #ident;
                     #ident = tonumber(#ident);
-                    if #ident == () || math::floor(#ident) != #ident {
-                        return error(concat!(#msg, r#type(#tmp)));
-                    }
+                    assert(#ident != () && math::floor(#ident) == #ident, concat!(#msg, r#type(#tmp)));
                 }),
                 LuaType::String => parse_quote_spanned!(span => {
-                    #init
+                    #prelude
                     if r#type(#ident) == "number" {
                         #ident = tostring(#ident);
-                    } else if r#type(#ident) != "string" {
-                        return error(concat!(#msg, r#type(#ident)));
+                    } else {
+                        assert(r#type(#ident) == "string", concat!(#msg, r#type(#ident)));
                     }
                 }),
                 _ => parse_quote_spanned!(span => {
-                    #init
-                    if r#type(#ident) != #ty_str {
-                        return error(concat!(#msg, r#type(#ident)));
-                    }
+                    #prelude
+                    assert(r#type(#ident) == #ty_str, concat!(#msg, r#type(#ident)));
                 }),
             }
         }
diff --git a/crates/luaify/tests/test.rs b/crates/luaify/tests/test.rs
index 825595a..dfad447 100644
--- a/crates/luaify/tests/test.rs
+++ b/crates/luaify/tests/test.rs
@@ -81,7 +81,7 @@ fn local_fn() {
             fn check(self: string, arg: number) {}
             inner
         }),
-        r#"function()local function check(self,arg)do if type(self)=="number"then self=tostring(self);elseif type(self)~="string"then return error("string expected in \'self\', got "..type(self));end;end;do local _arg=arg;arg=tonumber(arg);if arg==nil then return error("number expected in \'arg\', got "..type(_arg));end;end;end;return inner;end"#
+        r#"function()local function check(self,arg)do if type(self)=="number"then self=tostring(self);else assert(type(self)=="string","string expected in \'self\', got "..type(self));end;end;do local _arg=arg;arg=tonumber(arg);assert(arg~=nil,"number expected in \'arg\', got "..type(_arg));end;end;return inner;end"#
     );
 }
 
@@ -212,19 +212,19 @@ fn type_checks() {
     assert_eq!(luaify!(|s| {}), r#"function(s)end"#);
     assert_eq!(
         luaify!(|s: table| {}),
-        r#"function(s)do if type(s)~="table"then return error("table expected in \'s\', got "..type(s));end;end;end"#
+        r#"function(s)do assert(type(s)=="table","table expected in \'s\', got "..type(s));end;end"#
     );
     assert_eq!(
         luaify!(|s| { s as string }),
-        r#"function(s)do if type(s)=="number"then s=tostring(s);elseif type(s)~="string"then return error("string expected in \'s\', got "..type(s));end;end;end"#
+        r#"function(s)do if type(s)=="number"then s=tostring(s);else assert(type(s)=="string","string expected in \'s\', got "..type(s));end;end;end"#
     );
     assert_eq!(
         luaify!(|s| { s as number }),
-        r#"function(s)do local _s=s;s=tonumber(s);if s==nil then return error("number expected in \'s\', got "..type(_s));end;end;end"#
+        r#"function(s)do local _s=s;s=tonumber(s);assert(s~=nil,"number expected in \'s\', got "..type(_s));end;end"#
     );
     assert_eq!(
         luaify!(|s| { s as nil }),
-        r#"function(s)do if s~=nil then return error("nil expected in \'s\', got "..type(s));end;end;end"#
+        r#"function(s)do assert(s==nil,"nil expected in \'s\', got "..type(s));end;end"#
     );
     assert_eq!(luaify!(|s| { s as any }), r#"function(s)do end;end"#);
 
@@ -234,7 +234,7 @@ fn type_checks() {
             ok as boolean;
             res as nil;
         }),
-        r#"function(s)local ok,res=coroutine.yield(thread);do if type(ok)~="boolean"then return error("boolean expected in \'ok\', got "..type(ok));end;end;do if res~=nil then return error("nil expected in \'res\', got "..type(res));end;end;end"#
+        r#"function(s)local ok,res=coroutine.yield(thread);do assert(type(ok)=="boolean","boolean expected in \'ok\', got "..type(ok));end;do assert(res==nil,"nil expected in \'res\', got "..type(res));end;end"#
     );
 }