diff --git a/CHANGELOG.md b/CHANGELOG.md
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -1,3 +1,9 @@
+0.4.0.2
+----
+
+* Improvement around unhelpful error being thrown when CLI Config Map didn't
+  contain a value on a required (by code) field
+
 0.4.0.1
 ----
 
diff --git a/etc.cabal b/etc.cabal
--- a/etc.cabal
+++ b/etc.cabal
@@ -1,6 +1,6 @@
 cabal-version: >=1.10
 name: etc
-version: 0.4.0.1
+version: 0.4.0.2
 license: MIT
 license-file: LICENSE
 copyright: 2017, 2018 Roman Gonzalez
diff --git a/src/System/Etc/Internal/Config.hs b/src/System/Etc/Internal/Config.hs
--- a/src/System/Etc/Internal/Config.hs
+++ b/src/System/Etc/Internal/Config.hs
@@ -20,7 +20,7 @@
 configValueToJsonObject :: ConfigValue -> JSON.Value
 configValueToJsonObject configValue = case configValue of
   ConfigValue sources -> case Set.maxView sources of
-    Nothing          -> error "this should not happen"
+    Nothing          -> JSON.Null
 
     Just (source, _) -> fromValue $ value source
 
diff --git a/src/System/Etc/Internal/Extra/Printer.hs b/src/System/Etc/Internal/Extra/Printer.hs
--- a/src/System/Etc/Internal/Extra/Printer.hs
+++ b/src/System/Etc/Internal/Extra/Printer.hs
@@ -164,7 +164,7 @@
               --   - Value 2
               --   - Value 3
               --
-              return $ sourceDoc <$$> (indent 2 $ align (vsep multipleValues))
+              return $ sourceDoc <$$> indent 2 (align (vsep multipleValues))
       in  case eSourceDocs of
             Left  err -> throwM $ InvalidConfiguration (Just keyPath) err
 
@@ -207,7 +207,7 @@
   in
     do
       result <- loop [] configMap
-      return $ (hcat $ intersperse (linebreak <> linebreak) $ result) <> linebreak
+      return $ hcat (intersperse (linebreak <> linebreak) result) <> linebreak
 
 
 renderConfigColor :: MonadThrow m => Config -> m Doc
diff --git a/src/System/Etc/Internal/Resolver/Env.hs b/src/System/Etc/Internal/Resolver/Env.hs
--- a/src/System/Etc/Internal/Resolver/Env.hs
+++ b/src/System/Etc/Internal/Resolver/Env.hs
@@ -20,7 +20,7 @@
   -> Spec.ConfigSources cmd
   -> Maybe ConfigSource
 resolveEnvVarSource lookupEnv configValueType isSensitive specSources =
-  let envTextToJSON envValue = Spec.parseBytesToConfigValueJSON configValueType envValue
+  let envTextToJSON = Spec.parseBytesToConfigValueJSON configValueType
 
       toEnvSource varname envValue =
         Env varname . markAsSensitive isSensitive <$> envTextToJSON envValue
diff --git a/src/System/Etc/Internal/Spec/Types.hs b/src/System/Etc/Internal/Spec/Types.hs
--- a/src/System/Etc/Internal/Spec/Types.hs
+++ b/src/System/Etc/Internal/Spec/Types.hs
@@ -273,7 +273,7 @@
   (JSON.Bool{}  , CVTSingle CVTBool  ) -> True
   (JSON.Object{}, CVTSingle CVTObject) -> True
   (JSON.Array arr, CVTArray inner) ->
-    if null arr then True else all (flip matchesConfigValueType (CVTSingle inner)) arr
+    if null arr then True else all (`matchesConfigValueType` (CVTSingle inner)) arr
   _ -> False
 
 assertMatchingConfigValueType :: Monad m => JSON.Value -> ConfigValueType -> m ()
diff --git a/test/System/Etc/Resolver/Cli/PlainTest.hs b/test/System/Etc/Resolver/Cli/PlainTest.hs
--- a/test/System/Etc/Resolver/Cli/PlainTest.hs
+++ b/test/System/Etc/Resolver/Cli/PlainTest.hs
@@ -6,6 +6,9 @@
 import           RIO
 import qualified RIO.Set as Set
 
+import           Data.Aeson ((.:))
+import qualified Data.Aeson as JSON
+
 import Test.Tasty       (TestTree, testGroup)
 import Test.Tasty.HUnit (assertBool, assertEqual, assertFailure, testCase)
 
@@ -15,25 +18,42 @@
 resolver_tests = testGroup
   "resolver"
   [ testCase "throws an error when input type does not match with spec type" $ do
-      let input = mconcat
-            [ "{ \"etc/entries\": {"
-            , "    \"greeting\": {"
-            , "      \"etc/spec\": {"
-            , "        \"type\": \"[number]\""
-            , "        , \"cli\": {"
-            , "            \"input\": \"option\""
-            , "          , \"short\": \"g\""
-            , "          , \"long\": \"greeting\""
-            , "          , \"required\": true"
-            , "}}}}}"
-            ]
-      (spec :: SUT.ConfigSpec ()) <- SUT.parseConfigSpec input
-      eConfig <- try $ SUT.resolvePlainCliPure spec "program" ["-g", "hello world"]
+    let input = mconcat
+          [ "{ \"etc/entries\": {"
+          , "    \"greeting\": {"
+          , "      \"etc/spec\": {"
+          , "        \"type\": \"[number]\""
+          , "        , \"cli\": {"
+          , "            \"input\": \"option\""
+          , "          , \"short\": \"g\""
+          , "          , \"long\": \"greeting\""
+          , "          , \"required\": true"
+          , "}}}}}"
+          ]
+    (spec :: SUT.ConfigSpec ()) <- SUT.parseConfigSpec input
+    eConfig <- try $ SUT.resolvePlainCliPure spec "program" ["-g", "hello world"]
 
-      case eConfig of
-        Left SUT.CliEvalExited{} -> assertBool "" True
+    case eConfig of
+      Left SUT.CliEvalExited{} -> assertBool "" True
+      _ ->
+        assertFailure $ "Expecting CliEvalExited error; got this instead " <> show eConfig
+  , testCase "throws an error when entry is not given and is requested" $ do
+    let
+      input
+        = "{\"etc/entries\":{\"database\":{\"username\": {\"etc/spec\": {\"type\": \"string\", \"cli\": {\"input\": \"option\", \"long\": \"username\", \"required\": false}}}, \"password\": \"abc-123\"}}}"
+
+    (spec :: SUT.ConfigSpec ()) <- SUT.parseConfigSpec input
+    config                      <- SUT.resolvePlainCliPure spec "program" []
+    let parseDb = JSON.withObject "Database"
+          $ \obj -> (,) <$> obj .: "username" <*> obj .: "password"
+
+    case SUT.getConfigValueWith parseDb ["database"] config of
+      Left err -> case fromException err of
+        Just (SUT.InvalidConfiguration key _) ->
+          assertEqual "expecting key to be database, but wasn't" (Just "database") key
         _ ->
-          assertFailure $ "Expecting CliEvalExited error; got this instead " <> show eConfig
+          assertFailure $ "expecting InvalidConfiguration; got something else: " <> show err
+      Right (_ :: (Text, Text)) -> assertFailure "expecting error; got none"
   ]
 
 option_tests :: TestTree