diff --git a/src/interpreter/memory.rs b/src/interpreter/memory.rs
index b408e8e..eca5961 100644
--- a/src/interpreter/memory.rs
+++ b/src/interpreter/memory.rs
@@ -208,7 +208,7 @@ mod tests {
 	use elements::MemoryType;
 	use std::sync::Arc;
 
-	fn create_memory(initial_content: &[u8]) -> Arc<MemoryInstance<DummyUserError>> {
+	fn create_memory(initial_content: &[u8]) -> Arc<MemoryInstance> {
 		let mem = MemoryInstance::new(&MemoryType::new(1, Some(1)))
 			.expect("MemoryInstance created successfuly");
 		mem.set(0, initial_content).expect("Successful initialize the memory");
@@ -269,7 +269,7 @@ mod tests {
 
 	#[test]
 	fn get_into() {
-		let mem = MemoryInstance::<DummyUserError>::new(&MemoryType::new(1, None)).expect("memory instance creation should not fail");
+		let mem = MemoryInstance::new(&MemoryType::new(1, None)).expect("memory instance creation should not fail");
 		mem.set(6, &[13, 17, 129]).expect("memory set should not fail");
 
 		let mut data = [0u8; 2];
diff --git a/src/interpreter/tests/basics.rs b/src/interpreter/tests/basics.rs
index 7235e5f..178b7ef 100644
--- a/src/interpreter/tests/basics.rs
+++ b/src/interpreter/tests/basics.rs
@@ -129,12 +129,12 @@ struct MeasuredVariable {
 	pub val: i32,
 }
 
-impl ExternalVariableValue<UserErrorWithCode> for MeasuredVariable {
+impl ExternalVariableValue for MeasuredVariable {
 	fn get(&self) -> RuntimeValue {
 		RuntimeValue::I32(self.val)
 	}
 
-	fn set(&mut self, val: RuntimeValue) -> Result<(), Error<UserErrorWithCode>> {
+	fn set(&mut self, val: RuntimeValue) -> Result<(), Error> {
 		self.val = val.try_into()?;
 		Ok(())
 	}
@@ -156,12 +156,12 @@ impl UserError for UserErrorWithCode {}
 
 // user function executor
 struct FunctionExecutor {
-	pub memory: Arc<MemoryInstance<UserErrorWithCode>>,
+	pub memory: Arc<MemoryInstance>,
 	pub values: Vec<i32>,
 }
 
-impl UserFunctionExecutor<UserErrorWithCode> for FunctionExecutor {
-	fn execute(&mut self, name: &str, context: CallerContext<UserErrorWithCode>) -> Result<Option<RuntimeValue>, Error<UserErrorWithCode>> {
+impl UserFunctionExecutor for FunctionExecutor {
+	fn execute(&mut self, name: &str, context: CallerContext) -> Result<Option<RuntimeValue>, Error> {
 		match name {
 			"add" => {
 				let memory_value = self.memory.get(0, 1).unwrap()[0];
@@ -259,14 +259,14 @@ fn native_env_function_own_memory() {
 	let program = ProgramInstance::new().unwrap();
 
 	struct OwnMemoryReference {
-		pub memory: RefCell<Option<Arc<MemoryInstance<UserErrorWithCode>>>>,
+		pub memory: RefCell<Option<Arc<MemoryInstance>>>,
 	}
 	struct OwnMemoryExecutor {
 		pub memory_ref: Arc<OwnMemoryReference>,
 	}
 
-	impl UserFunctionExecutor<UserErrorWithCode> for OwnMemoryExecutor {
-		fn execute(&mut self, name: &str, context: CallerContext<UserErrorWithCode>) -> Result<Option<RuntimeValue>, Error<UserErrorWithCode>> {
+	impl UserFunctionExecutor for OwnMemoryExecutor {
+		fn execute(&mut self, name: &str, context: CallerContext) -> Result<Option<RuntimeValue>, Error> {
 			match name {
 				"add" => {
 					let memory = self.memory_ref.memory.borrow_mut().as_ref().expect("initialized before execution; qed").clone();