diff --git a/src/Aws/Lambda/Runtime.hs b/src/Aws/Lambda/Runtime.hs
index 2ce9114..c0758d5 100644
--- a/src/Aws/Lambda/Runtime.hs
+++ b/src/Aws/Lambda/Runtime.hs
@@ -43,12 +43,14 @@ runLambda initializeCustomContext callback = do
     -- Purposefully shadowing to prevent using the initial "empty" context
     context <- Context.setEventData context event
 
-    ( ( ( invokeAndRun callback manager lambdaApi event context
-            `Checked.catch` \err -> Publish.parsingError err lambdaApi context manager
+    ( ( ( ( invokeAndRun callback manager lambdaApi event context
+              `Checked.catch` \err -> Publish.parsingError err lambdaApi context manager
+          )
+            `Checked.catch` \err -> Publish.invocationError err lambdaApi context manager
         )
-          `Checked.catch` \err -> Publish.invocationError err lambdaApi context manager
+          `Checked.catch` \(err :: Error.EnvironmentVariableNotSet) -> Publish.runtimeInitError err lambdaApi context manager
       )
-        `Checked.catch` \(err :: Error.EnvironmentVariableNotSet) -> Publish.runtimeInitError err lambdaApi context manager
+        `Unchecked.catch` \(err :: Error.HandlerNotFound) -> Publish.handlerNotFoundError err lambdaApi context manager
       )
       `Unchecked.catch` \err -> Publish.invocationError err lambdaApi context manager
 
diff --git a/src/Aws/Lambda/Runtime/Error.hs b/src/Aws/Lambda/Runtime/Error.hs
index 1ea1cde..4ce30ed 100644
--- a/src/Aws/Lambda/Runtime/Error.hs
+++ b/src/Aws/Lambda/Runtime/Error.hs
@@ -2,6 +2,7 @@
 module Aws.Lambda.Runtime.Error
   ( EnvironmentVariableNotSet (..),
     Parsing (..),
+    HandlerNotFound (..),
     Invocation (..),
   )
 where
@@ -36,6 +37,16 @@ instance ToJSON Parsing where
         "errorMessage" .= ("Could not parse '" <> valueName <> "': " <> errorMessage)
       ]
 
+newtype HandlerNotFound = HandlerNotFound Text
+  deriving (Show, Exception)
+
+instance ToJSON HandlerNotFound where
+  toJSON (HandlerNotFound handler) =
+    object
+      [ "errorType" .= ("Runtime.HandlerNotFound" :: Text),
+        "errorMessage" .= ("Could not find handler '" <> handler <> "'.")
+      ]
+
 newtype Invocation
   = Invocation LBS.ByteString
   deriving (Show, Exception)
diff --git a/src/Aws/Lambda/Runtime/Publish.hs b/src/Aws/Lambda/Runtime/Publish.hs
index 5032231..ccab487 100644
--- a/src/Aws/Lambda/Runtime/Publish.hs
+++ b/src/Aws/Lambda/Runtime/Publish.hs
@@ -6,6 +6,7 @@ module Aws.Lambda.Runtime.Publish
   ( result,
     invocationError,
     parsingError,
+    handlerNotFoundError,
     runtimeInitError,
   )
 where
@@ -56,6 +57,14 @@ parsingError err lambdaApi context =
     (Endpoints.invocationError lambdaApi $ awsRequestId context)
     context
 
+-- | Publishes a HandlerNotFound error back to AWS Lambda
+handlerNotFoundError :: Error.HandlerNotFound -> Text -> Context context -> Http.Manager -> IO ()
+handlerNotFoundError err lambdaApi context =
+  publish
+    (encode err)
+    (Endpoints.invocationError lambdaApi $ awsRequestId context)
+    context
+
 -- | Publishes a runtime initialization error back to AWS Lambda
 runtimeInitError :: ToJSON err => err -> Text -> Context context -> Http.Manager -> IO ()
 runtimeInitError err lambdaApi =
diff --git a/src/Aws/Lambda/Setup.hs b/src/Aws/Lambda/Setup.hs
index 31555cd..c744774 100644
--- a/src/Aws/Lambda/Setup.hs
+++ b/src/Aws/Lambda/Setup.hs
@@ -64,6 +64,7 @@ import qualified Data.Text as Text
 import Data.Typeable (Typeable)
 import GHC.IO.Handle.FD (stderr)
 import GHC.IO.Handle.Text (hPutStr)
+import qualified Aws.Lambda.Runtime.Error as Error
 
 type Handlers handlerType m context request response error =
   HM.HashMap HandlerName (Handler handlerType m context request response error)
@@ -129,9 +130,7 @@ run dispatcherOptions mToIO handlers (LambdaOptions eventObject functionHandler
   case HM.lookup functionHandler asIOCallbacks of
     Just handlerToCall -> handlerToCall
     Nothing ->
-      throwM $
-        userError $
-          "Could not find handler '" <> (Text.unpack . unHandlerName $ functionHandler) <> "'."
+      throwM $ Error.HandlerNotFound (unHandlerName functionHandler)
 
 addStandaloneLambdaHandler ::
   HandlerName ->