diff --git a/lambda-runtime-client/src/error.rs b/lambda-runtime-client/src/error.rs
index 6dd5356e..25d12492 100644
--- a/lambda-runtime-client/src/error.rs
+++ b/lambda-runtime-client/src/error.rs
@@ -9,30 +9,30 @@ use hyper;
 use serde_derive::Serialize;
 use serde_json;
 
-/// Error type description for the `ErrorResponse` event. This type should be returned
-/// for errors that were handled by the function code or framework.
-pub const ERROR_TYPE_HANDLED: &str = "Handled";
-/// Error type description for the `ErrorResponse` event. This type is used for unhandled,
-/// unexpcted errors.
-pub const ERROR_TYPE_UNHANDLED: &str = "Unhandled";
+/// Error type description for the `ErrorResponse` event.
+#[derive(Serialize)]
+pub enum ErrorType {
+    /// This type should be returned
+    /// for errors that were handled by the function code or framework.
+    Handled,
+    /// This type is used for unhandled,
+    /// unexpcted errors.
+    Unhandled,
+}
 
 /// This object is used to generate requests to the Lambda Runtime APIs.
 /// It is used for both the error response APIs and fail init calls.
 /// custom error types should implement the `RuntimeError` trait and return
 /// this object to be compatible with the APIs.
 #[derive(Serialize)]
+#[serde(rename_all="camelCase")]
 pub struct ErrorResponse {
     /// The error message generated by the application.
-    #[serde(rename = "errorMessage")]
     pub error_message: String,
-    /// The error type for Lambda. This can be `Handled` or `Unhandled`.
-    /// Developers can use the `ERROR_TYPE_HANDLED` and `ERROR_TYPE_UNHANDLED`
-    /// constants to populate this field.
-    #[serde(rename = "errorType")]
-    pub error_type: String,
+    /// The error type for Lambda.
+    pub error_type: ErrorType,
     /// The stack trace for the exception as vector of strings. In the framework,
     /// this value is automatically populated using the `backtrace` crate.
-    #[serde(rename = "stackTrace")]
     pub stack_trace: Option<Vec<String>>,
 }
 
@@ -45,10 +45,10 @@ impl ErrorResponse {
     ///
     /// # Return
     /// A populated `RuntimeError` object that can be used with the Lambda Runtime API.
-    pub fn handled(message: String) -> ErrorResponse {
+    pub fn handled<M>(message: M) -> ErrorResponse where M: Into<String> {
         ErrorResponse {
-            error_message: message,
-            error_type: String::from(ERROR_TYPE_HANDLED),
+            error_message: message.into(),
+            error_type: ErrorType::Handled,
             stack_trace: Option::default(),
         }
     }
@@ -61,10 +61,10 @@ impl ErrorResponse {
     ///
     /// # Return
     /// A populated `RuntimeError` object that can be used with the Lambda Runtime API.
-    pub fn unhandled(message: String) -> ErrorResponse {
+    pub fn unhandled<M>(message: M) -> ErrorResponse where M: Into<String> {
         ErrorResponse {
-            error_message: message,
-            error_type: String::from(ERROR_TYPE_UNHANDLED),
+            error_message: message.into(),
+            error_type: ErrorType::Unhandled,
             stack_trace: Option::default(),
         }
     }
@@ -182,3 +182,24 @@ impl RuntimeApiError for ApiError {
         err
     }
 }
+
+#[cfg(test)]
+mod tests {
+    use super::ErrorResponse;
+
+    #[test]
+    fn handled_error_response_serializes() {
+        assert_eq!(
+            serde_json::to_string(&ErrorResponse::handled("💀")).expect("failed to serialize ErrorResponse"),
+            r#"{"errorMessage":"💀","errorType":"Handled","stackTrace":null}"#
+        )
+    }
+
+    #[test]
+    fn unhandled_error_response_serializes() {
+        assert_eq!(
+            serde_json::to_string(&ErrorResponse::unhandled("💀")).expect("failed to serialize ErrorResponse"),
+            r#"{"errorMessage":"💀","errorType":"Unhandled","stackTrace":null}"#
+        )
+    }
+}
\ No newline at end of file
diff --git a/lambda-runtime/src/error.rs b/lambda-runtime/src/error.rs
index 975d7919..3c6b0f76 100644
--- a/lambda-runtime/src/error.rs
+++ b/lambda-runtime/src/error.rs
@@ -70,7 +70,7 @@ impl error::RuntimeApiError for RuntimeError {
         let backtrace = format!("{:?}", self.stack_trace);
         error::ErrorResponse {
             error_message: String::from(self.description()),
-            error_type: String::from(error::ERROR_TYPE_HANDLED),
+            error_type: error::ErrorType::Handled,
             stack_trace: Option::from(backtrace.lines().map(|s| s.to_string()).collect::<Vec<String>>()),
         }
     }
@@ -173,7 +173,7 @@ impl error::RuntimeApiError for HandlerError {
         let backtrace = format!("{:?}", self.backtrace);
         error::ErrorResponse {
             error_message: String::from(self.description()),
-            error_type: String::from(error::ERROR_TYPE_HANDLED),
+            error_type: error::ErrorType::Handled,
             stack_trace: Option::from(backtrace.lines().map(|s| s.to_string()).collect::<Vec<String>>()),
         }
     }