diff --git a/src/nimble.nim b/src/nimble.nim
index 01bd30c..4d3ef24 100644
--- a/src/nimble.nim
+++ b/src/nimble.nim
@@ -89,7 +89,7 @@ Options:
   -n, --reject                    Reject all interactive prompts.
       --ver                       Query remote server for package version
                                   information when searching or listing packages
-      --nimbledir dirname         Set the Nimble directory.
+      --nimbleDir dirname         Set the Nimble directory.
 
 For more information read the Github readme:
   https://github.com/nim-lang/nimble#readme
@@ -227,15 +227,16 @@ proc parseCmdLine(): Options =
         else:
           result.action.compileOptions.add("--" & key & ":" & val)
       else:
-        case key
+        case key.normalize()
         of "help", "h": writeHelp()
         of "version", "v": writeVersion()
         of "accept", "y": result.forcePrompts = forcePromptYes
         of "reject", "n": result.forcePrompts = forcePromptNo
         of "ver": result.queryVersions = true
-        of "nimbleDir": result.config.nimbleDir = val # overrides option from file
+        of "nimbledir": result.config.nimbleDir = val # overrides option from file
         of "installed", "i": result.queryInstalled = true
-        else: discard
+        else:
+          raise newException(NimbleError, "Unknown option: --" & key)
     of cmdEnd: assert(false) # cannot happen
   if result.action.typ == actionNil:
     writeHelp()