diff --git a/src/command.ts b/src/command.ts
index 119ae54..79b4858 100644
--- a/src/command.ts
+++ b/src/command.ts
@@ -12,6 +12,7 @@ import {
   OPT_SHORT_PREFIX,
   NEGATE_SHORT_PREFIX,
   Prefixes,
+  FlagConfig,
 } from './option'
 import { DeepRequired, setOrPush, deepMerge } from './utils'
 import { MassargExample, ExampleConfig } from './example'
@@ -99,6 +100,10 @@ export class MassargCommand<Args extends ArgsObject = ArgsObject> {
   }
 
   get optionPrefixes(): Prefixes {
+    return this.getPrefixes()
+  }
+
+  private getPrefixes(): Prefixes {
     return {
       optionPrefix: this.optionPrefix,
       aliasPrefix: this.optionAliasPrefix,
@@ -177,11 +182,9 @@ export class MassargCommand<Args extends ArgsObject = ArgsObject> {
    * or by prefixing the alias with `^` instead of `-`. This is configurable via the command's
    * configuration.
    */
-  flag(config: Omit<OptionConfig<boolean>, 'parse' | 'isDefault'>): MassargCommand<Args>
+  flag(config: FlagConfig): MassargCommand<Args>
   flag(config: MassargFlag): MassargCommand<Args>
-  flag(
-    config: Omit<OptionConfig<boolean>, 'parse' | 'isDefault'> | MassargFlag,
-  ): MassargCommand<Args> {
+  flag(config: FlagConfig | MassargFlag): MassargCommand<Args> {
     try {
       const flag = config instanceof MassargFlag ? config : new MassargFlag(config)
       const existing = this.options.find((c) => c.name === flag.name)
@@ -320,15 +323,17 @@ export class MassargCommand<Args extends ArgsObject = ArgsObject> {
   }
 
   private parseOption(arg: string, argv: string[]) {
-    const option = this.options.find((o) => o._match(arg, this.optionPrefixes))
+    const prefixes = { ...this.optionPrefixes }
+    const option = this.options.find((o) => o._match(arg, prefixes))
     if (!option) {
       throw new ValidationError({
-        path: [MassargOption.findNameInArg(arg, this.optionPrefixes)],
+        path: [MassargOption.findNameInArg(arg, prefixes)],
         code: 'unknown_option',
         message: 'Unknown option',
       })
     }
-    const res = option._parseDetails([arg, ...argv], { ...this.args }, this.optionPrefixes)
+    const res = option.parseDetails([arg, ...argv], { ...this.args }, prefixes)
+
     this.args[res.key as keyof Args] = setOrPush<Args[keyof Args]>(
       res.value,
       this.args[res.key as keyof Args],
@@ -377,7 +382,7 @@ export class MassargCommand<Args extends ArgsObject = ArgsObject> {
     while (_argv.length) {
       const arg = _argv.shift()!
       // make sure option exists
-      const found = this.options.some((o) => o._isOption(arg, this.optionPrefixes))
+      const found = this.options.some((o) => o._isOption(arg, { ...this.optionPrefixes }))
       if (found) {
         _argv = this.parseOption(arg, _argv)
         _args = { ..._args, ...this.args }
diff --git a/src/help.ts b/src/help.ts
index 2756b2b..f5dc39e 100644
--- a/src/help.ts
+++ b/src/help.ts
@@ -214,9 +214,9 @@ export class HelpGenerator {
     }
     const maxNameLength = this.config.useGlobalTableColumns
       ? Math.max(
-        getMaxNameLength(entry.options.map((e) => getItemDetails(e, optionOptions))),
-        getMaxNameLength(entry.commands.map((e) => getItemDetails(e, commandOptions))),
-      )
+          getMaxNameLength(entry.options.map((e) => getItemDetails(e, optionOptions))),
+          getMaxNameLength(entry.commands.map((e) => getItemDetails(e, commandOptions))),
+        )
       : undefined
     const options = generateHelpTable(entry.options, optionOptions, maxNameLength).trimEnd()
     const commands = generateHelpTable(entry.commands, commandOptions, maxNameLength).trimEnd()
@@ -228,21 +228,21 @@ export class HelpGenerator {
             _wrap(format(description, this.config.exampleOptions.descriptionStyle), 4),
           ],
           input &&
-          _wrap(
-            format(
-              [this.config.exampleOptions.inputPrefix, input].filter(Boolean).join(' '),
-              this.config.exampleOptions.inputStyle,
+            _wrap(
+              format(
+                [this.config.exampleOptions.inputPrefix, input].filter(Boolean).join(' '),
+                this.config.exampleOptions.inputStyle,
+              ),
+              4,
             ),
-            4,
-          ),
           output &&
-          _wrap(
-            format(
-              [this.config.exampleOptions.outputPrefix, output].filter(Boolean).join(' '),
-              this.config.exampleOptions.outputStyle,
+            _wrap(
+              format(
+                [this.config.exampleOptions.outputPrefix, output].filter(Boolean).join(' '),
+                this.config.exampleOptions.outputStyle,
+              ),
+              4,
             ),
-            4,
-          ),
         )
       })
       .join('\n')
@@ -253,17 +253,17 @@ export class HelpGenerator {
         _wrap(
           usageText
             ? strConcat(
-              format('Usage:', this.config.usageStyle.prefix),
-              format(usageText, this.config.usageStyle.main),
-            )
+                format('Usage:', this.config.usageStyle.prefix),
+                format(usageText, this.config.usageStyle.main),
+              )
             : [
-              format(`Usage:`, this.config.usageStyle.prefix),
-              format(entry.name, this.config.usageStyle.main),
-              commands.length && format('[command]', this.config.usageStyle.command),
-              options.length && format('[options]', this.config.usageStyle.options),
-            ]
-              .filter(Boolean)
-              .join(' '),
+                format(`Usage:`, this.config.usageStyle.prefix),
+                format(entry.name, this.config.usageStyle.main),
+                commands.length && format('[command]', this.config.usageStyle.command),
+                options.length && format('[options]', this.config.usageStyle.options),
+              ]
+                .filter(Boolean)
+                .join(' '),
         ),
         headerText.length && ['', format(headerText, this.config.descriptionStyle)],
         entry.description.length && [
@@ -271,27 +271,27 @@ export class HelpGenerator {
           _wrap(format(entry.description, this.config.descriptionStyle)),
         ],
         commands.length &&
-        indent([
-          '',
-          format(
-            entry.parent ? `Commands for ${entry.name}:` : 'Commands:',
-            this.config.subtitleStyle,
-          ),
-          '',
-          indent(commands),
-        ]),
+          indent([
+            '',
+            format(
+              entry.parent ? `Commands for ${entry.name}:` : 'Commands:',
+              this.config.subtitleStyle,
+            ),
+            '',
+            indent(commands),
+          ]),
         options.length &&
-        indent([
-          '',
-          format(
-            entry.parent ? `Options for ${entry.name}:` : 'Options:',
-            this.config.subtitleStyle,
-          ),
-          '',
-          indent(options),
-        ]),
+          indent([
+            '',
+            format(
+              entry.parent ? `Options for ${entry.name}:` : 'Options:',
+              this.config.subtitleStyle,
+            ),
+            '',
+            indent(options),
+          ]),
         examples.length &&
-        indent(['', format('Examples:', this.config.subtitleStyle), '', indent(examples)]),
+          indent(['', format('Examples:', this.config.subtitleStyle), '', indent(examples)]),
         footerText.length && ['', _wrap(format(footerText, this.config.descriptionStyle))],
       ) + '\n'
     )
diff --git a/src/option.ts b/src/option.ts
index 3854c25..e5cbf41 100644
--- a/src/option.ts
+++ b/src/option.ts
@@ -50,12 +50,14 @@ export type OptionConfig<T = unknown, Args extends ArgsObject = ArgsObject> = z.
   ReturnType<typeof OptionConfig<T, Args>>
 >
 
-export const FlagConfig = OptionConfig<boolean>(z.any()).merge(
-  z.object({
-    /** Whether the flag can be negated, e.g. `--no-verbose` */
-    negatable: z.boolean().optional(),
-  }),
-)
+export const FlagConfig = OptionConfig<boolean>(z.any())
+  .omit({ parse: true, isDefault: true })
+  .merge(
+    z.object({
+      /** Whether the flag can be negated, e.g. `--no-verbose` */
+      negatable: z.boolean().optional(),
+    }),
+  )
 export type FlagConfig = z.infer<typeof FlagConfig>
 
 export type Parser<Args extends ArgsObject = ArgsObject, OptionType extends any = any> = (
@@ -99,7 +101,7 @@ export type ArrayOptionConfig<T = unknown> = z.infer<
 // TODO turn to options
 export const OPT_FULL_PREFIX = '--'
 export const OPT_SHORT_PREFIX = '-'
-export const NEGATE_FULL_PREFIX = 'no-'
+export const NEGATE_FULL_PREFIX = '--no-'
 export const NEGATE_SHORT_PREFIX = '^'
 
 export type Prefixes = {
@@ -172,8 +174,7 @@ export class MassargOption<OptionType extends any = unknown, Args extends ArgsOb
     return this.outputName || toCamelCase(this.name)
   }
 
-  _parseDetails(argv: string[], options: ArgsObject, prefixes: Prefixes): ArgvValue<OptionType> {
-    // TODO: support --option=value
+  parseDetails(argv: string[], options: ArgsObject, prefixes: Prefixes): ArgvValue<OptionType> {
     let input = ''
     try {
       if (!this._match(argv[0], prefixes)) {
@@ -221,25 +222,21 @@ export class MassargOption<OptionType extends any = unknown, Args extends ArgsOb
 
   static findNameInArg(arg: string, prefixes: Prefixes): string {
     const { optionPrefix, aliasPrefix, negateFlagPrefix, negateAliasPrefix } = prefixes
-    if (arg.startsWith(optionPrefix)) {
-      // negate full prefix
-      if (arg.startsWith(negateFlagPrefix)) {
-        return arg.slice(negateFlagPrefix.length)
-      }
-      return arg.slice(optionPrefix.length)
-    }
     // negate full prefix
     if (arg.startsWith(negateFlagPrefix)) {
       return arg.slice(negateFlagPrefix.length)
     }
-    // short prefix
-    if (arg.startsWith(aliasPrefix) || arg.startsWith(negateAliasPrefix)) {
-      return arg.slice(aliasPrefix.length)
+    if (arg.startsWith(optionPrefix)) {
+      return arg.slice(optionPrefix.length)
     }
     // negate short prefix
     if (arg.startsWith(negateAliasPrefix)) {
       return arg.slice(negateAliasPrefix.length)
     }
+    // short prefix
+    if (arg.startsWith(aliasPrefix) || arg.startsWith(negateAliasPrefix)) {
+      return arg.slice(aliasPrefix.length)
+    }
     return '<blank>'
   }
 }
@@ -268,9 +265,9 @@ export class MassargNumber extends MassargOption<number> {
     })
   }
 
-  _parseDetails(argv: string[], options: ArgsObject, prefixes: Prefixes): ArgvValue<number> {
+  parseDetails(argv: string[], options: ArgsObject, prefixes: Prefixes): ArgvValue<number> {
     try {
-      const { argv: _argv, value } = super._parseDetails(argv, options, prefixes)
+      const { argv: _argv, value } = super.parseDetails(argv, options, prefixes)
       if (isNaN(value)) {
         throw new ParseError({
           path: [this.name],
@@ -326,7 +323,7 @@ export class MassargFlag extends MassargOption<boolean> {
     this.negatable = options.negatable ?? false
   }
 
-  _parseDetails(argv: string[], prefixes: Prefixes): ArgvValue<boolean> {
+  parseDetails(argv: string[], options: ArgsObject, prefixes: Prefixes): ArgvValue<boolean> {
     try {
       const isNegation =
         argv[0]?.startsWith(prefixes.negateAliasPrefix) ||
@@ -350,9 +347,9 @@ export class MassargFlag extends MassargOption<boolean> {
 
       argv.shift()
       if (isNegation) {
-        return { key: this.name, value: false, argv }
+        return { key: this.getOutputName(), value: false, argv }
       }
-      return { key: this.name, value: true, argv }
+      return { key: this.getOutputName(), value: true, argv }
     } catch (e) {
       if (isZodError(e)) {
         throw new ParseError({
diff --git a/src/utils.ts b/src/utils.ts
index 0d39830..55e8bd5 100644
--- a/src/utils.ts
+++ b/src/utils.ts
@@ -91,15 +91,17 @@ export function deepMerge<T1, T2>(obj1: T1, obj2: T2): NonNullable<T1> & NonNull
  * regular spaced strings.
  */
 export function splitWords(str: string): string[] {
-  return str
-    .replace(/([a-z])([A-Z])/g, '$1 $2')
-    .replace(/([a-zA-Z])([0-9])/g, '$1 $2')
-    .replace(/([0-9])([a-zA-Z])/g, '$1 $2')
-    .replace(/([a-z])([_-])/g, '$1 $2')
-    .replace(/([_-])([a-zA-Z])/g, '$1 $2')
-    .split(/[_-]/)
-    .map((s) => s.trim())
-    .filter(Boolean)
+  return (
+    str
+      .replace(/([a-z])([A-Z])/g, '$1 $2')
+      // .replace(/([a-zA-Z])([0-9])/g, '$1 $2')
+      .replace(/([0-9])([a-zA-Z])/g, '$1 $2')
+      .replace(/([a-z])([_-])/g, '$1 $2')
+      .replace(/([_-])([a-zA-Z])/g, '$1 $2')
+      .split(/[_-]/)
+      .map((s) => s.trim())
+      .filter(Boolean)
+  )
 }
 
 export function toCamelCase(str: string): string {
diff --git a/test/option.test.ts b/test/option.test.ts
index fa57c15..fd6262d 100644
--- a/test/option.test.ts
+++ b/test/option.test.ts
@@ -104,9 +104,20 @@ describe('flag', () => {
     ).toThrow('Expected string, received number')
   })
   describe('negation', () => {
-    test('default', () => {
+    test('no negation', () => {
       const command = massarg(opts).flag({ name: 'test2', description: 'test2', aliases: [] })
-      expect(command.getArgs(['--no-test2'])).toThrow('is not negatable')
+      expect(() => command.getArgs(['--no-test2'])).toThrow(
+        'test2: Option test2 cannot be negated (received: "--no-test2")',
+      )
+    })
+    test('negation', () => {
+      const command = massarg(opts).flag({
+        name: 'test2',
+        description: 'test2',
+        aliases: [],
+        negatable: true,
+      })
+      expect(command.getArgs(['--no-test2'])).toHaveProperty('test2', false)
     })
   })
 })