diff --git a/spec/src/run.rs b/spec/src/run.rs
index e85f833..a74b526 100644
--- a/spec/src/run.rs
+++ b/spec/src/run.rs
@@ -13,8 +13,8 @@ use wasmi::{
     GlobalInstance, GlobalRef, ImportResolver, ImportsBuilder,
     MemoryInstance, MemoryRef, ModuleImportResolver, ModuleInstance,
     ModuleRef, RuntimeValue, TableInstance, TableRef, ValueType,
-    load_from_buffer, LoadedModule, Signature, MemoryDescriptor, 
-    TableDescriptor, GlobalDescriptor, FuncInstance,
+    load_from_buffer, LoadedModule, Signature, MemoryDescriptor,
+    TableDescriptor, GlobalDescriptor, FuncInstance, RuntimeArgs,
 };
 
 #[derive(Debug)]
@@ -57,7 +57,7 @@ impl Externals for SpecModule {
     fn invoke_index(
         &mut self,
         index: usize,
-        args: &[RuntimeValue],
+        args: RuntimeArgs,
     ) -> Result<Option<RuntimeValue>, InterpreterError> {
         match index {
             PRINT_FUNC_INDEX => {
diff --git a/src/host.rs b/src/host.rs
index 4557f40..13e722f 100644
--- a/src/host.rs
+++ b/src/host.rs
@@ -3,6 +3,7 @@ use value::{RuntimeValue, TryInto};
 use Error;
 
 /// Safe wrapper for list of arguments
+#[derive(Debug)]
 pub struct RuntimeArgs<'a>(&'a [RuntimeValue]);
 
 impl<'a> From<&'a [RuntimeValue]> for RuntimeArgs<'a> {
@@ -94,4 +95,9 @@ mod tests {
 		assert_eq!(val, 0);
 	}
 
+	#[test]
+	fn i64_invalid_arg_cast() {
+		let args: RuntimeArgs = (&[RuntimeValue::I64(90534534545322)][..]).into();
+		assert!(args.nth::<i32>(0).is_err());
+	}
 }
\ No newline at end of file
diff --git a/src/tests/host.rs b/src/tests/host.rs
index 96570f3..7795753 100644
--- a/src/tests/host.rs
+++ b/src/tests/host.rs
@@ -1,8 +1,7 @@
 use {
 	Error, Signature, Externals, FuncInstance, FuncRef, HostError, ImportsBuilder,
 	MemoryInstance, MemoryRef, TableInstance, TableRef, ModuleImportResolver, ModuleInstance, ModuleRef,
-	RuntimeValue, TryInto, LoadedModule, load_from_buffer, TableDescriptor, MemoryDescriptor,
-	RuntimeArgs,
+	RuntimeValue, RuntimeArgs, LoadedModule, load_from_buffer, TableDescriptor, MemoryDescriptor,
 };
 use types::ValueType;
 use wabt::wat2wasm;