diff --git a/app/javascript/mastodon/features/compose/components/compose_form.js b/app/javascript/mastodon/features/compose/components/compose_form.js
index 6eb01123e..9f038e6fb 100644
--- a/app/javascript/mastodon/features/compose/components/compose_form.js
+++ b/app/javascript/mastodon/features/compose/components/compose_form.js
@@ -80,7 +80,7 @@ export default class ComposeForm extends ImmutablePureComponent {
     const { is_submitting, is_uploading, anyMedia } = this.props;
     const fulltext = [this.props.spoiler_text, countableText(this.props.text)].join('');
 
-    if (is_submitting || is_uploading || length(fulltext) > 500 || (fulltext.length !== 0 && fulltext.trim().length === 0 && !anyMedia)) {
+    if (is_submitting || is_uploading || length(fulltext) > 512 || (fulltext.length !== 0 && fulltext.trim().length === 0 && !anyMedia)) {
       return;
     }
 
@@ -156,7 +156,7 @@ export default class ComposeForm extends ImmutablePureComponent {
     const { intl, onPaste, showSearch, anyMedia } = this.props;
     const disabled = this.props.is_submitting;
     const text     = [this.props.spoiler_text, countableText(this.props.text)].join('');
-    const disabledButton = disabled || this.props.is_uploading || length(text) > 500 || (text.length !== 0 && text.trim().length === 0 && !anyMedia);
+    const disabledButton = disabled || this.props.is_uploading || length(text) > 512 || (text.length !== 0 && text.trim().length === 0 && !anyMedia);
     let publishText = '';
 
     if (this.props.privacy === 'private' || this.props.privacy === 'direct') {
@@ -208,7 +208,7 @@ export default class ComposeForm extends ImmutablePureComponent {
             <SensitiveButtonContainer />
             <SpoilerButtonContainer />
           </div>
-          <div className='character-counter__wrapper'><CharacterCounter max={500} text={text} /></div>
+          <div className='character-counter__wrapper'><CharacterCounter max={512} text={text} /></div>
         </div>
 
         <div className='compose-form__publish'>
diff --git a/app/validators/status_length_validator.rb b/app/validators/status_length_validator.rb
index ed5563f64..4d51fd3e1 100644
--- a/app/validators/status_length_validator.rb
+++ b/app/validators/status_length_validator.rb
@@ -1,7 +1,7 @@
 # frozen_string_literal: true
 
 class StatusLengthValidator < ActiveModel::Validator
-  MAX_CHARS = 500
+  MAX_CHARS = 512
 
   def validate(status)
     return unless status.local? && !status.reblog?