diff --git a/assets/base/i18n/en.json b/assets/base/i18n/en.json
index 057487627..15bb17e4e 100644
--- a/assets/base/i18n/en.json
+++ b/assets/base/i18n/en.json
@@ -453,6 +453,8 @@
   "mobile.share_extension.error_message": "An error has occurred while using the share extension.",
   "mobile.share_extension.error_title": "Extension Error",
   "mobile.share_extension.team": "Team",
+  "mobile.share_extension.too_long_message": "Character count: {count}/{max}",
+  "mobile.share_extension.too_long_title": "Message is too long",
   "mobile.sidebar_settings.permanent": "Permanent Sidebar",
   "mobile.sidebar_settings.permanent_description": "Keep the sidebar open permanently",
   "mobile.storage_permission_denied_description": "Upload files to your Mattermost instance. Open Settings to grant Mattermost Read and Write access to files on this device.",
diff --git a/share_extension/android/extension_post/extension_post.js b/share_extension/android/extension_post/extension_post.js
index b71c13094..ac90bd558 100644
--- a/share_extension/android/extension_post/extension_post.js
+++ b/share_extension/android/extension_post/extension_post.js
@@ -406,17 +406,34 @@ export default class ExtensionPost extends PureComponent {
     onPost = () => {
         const {channelId, files, value} = this.state;
         const {currentUserId} = this.props;
+        const {formatMessage} = this.context.intl;
 
-        const data = {
-            channelId,
-            currentUserId,
-            files,
-            token: this.token,
-            url: this.url,
-            value,
-        };
+        if (value.length > MAX_MESSAGE_LENGTH) {
+            Alert.alert(
+                formatMessage({
+                    id: 'mobile.share_extension.too_long_title',
+                    defaultMessage: 'Message is too long',
+                }),
+                formatMessage({
+                    id: 'mobile.share_extension.too_long_message',
+                    defaultMessage: 'Character count: {count}/{max}',
+                }, {
+                    count: value.length,
+                    max: MAX_MESSAGE_LENGTH,
+                })
+            );
+        } else {
+            const data = {
+                channelId,
+                currentUserId,
+                files,
+                token: this.token,
+                url: this.url,
+                value,
+            };
 
-        this.onClose(data);
+            this.onClose(data);
+        }
     };
 
     renderBody = () => {
@@ -435,7 +452,6 @@ export default class ExtensionPost extends PureComponent {
                 <TextInput
                     ref={this.getInputRef}
                     autoCapitalize='sentences'
-                    maxLength={MAX_MESSAGE_LENGTH}
                     multiline={true}
                     onBlur={this.handleBlur}
                     onChangeText={this.handleTextChange}
@@ -566,6 +582,29 @@ export default class ExtensionPost extends PureComponent {
         );
     };
 
+    lengthCounterColor = (count) => {
+        if (count < 0) {
+            return styles.textTooLong;
+        }
+        return styles.textLengthOk;
+    }
+
+    renderMessageLengthRemaining = () => {
+        const {value} = this.state;
+        const messageLengthRemaining = MAX_MESSAGE_LENGTH - value.length;
+
+        if (value.length === 0) {
+            return null;
+        }
+
+        const renderStyle = [styles.messageLengthRemaining, this.lengthCounterColor(messageLengthRemaining)];
+        return (
+            <Text style={renderStyle}>
+                {messageLengthRemaining}
+            </Text>
+        );
+    };
+
     render() {
         const {formatMessage} = this.context.intl;
         const {maxFileSize} = this.props;
@@ -610,6 +649,7 @@ export default class ExtensionPost extends PureComponent {
                     <View style={styles.wrapper}>
                         {this.renderBody()}
                         <View style={styles.flex}>
+                            {this.renderMessageLengthRemaining()}
                             {this.renderTeamButton()}
                             {this.renderChannelButton()}
                         </View>
@@ -654,6 +694,19 @@ const getStyleSheet = makeStyleSheetFromTheme((theme) => {
             flex: 1,
             padding: 15,
         },
+        messageLengthRemaining: {
+            paddingTop: 5,
+            paddingBottom: 5,
+            paddingLeft: 15,
+            paddingRight: 15,
+            opacity: 0.5,
+        },
+        textLengthOk: {
+            color: theme.centerChannelColor,
+        },
+        textTooLong: {
+            color: theme.errorTextColor,
+        },
         input: {
             flex: 1,
             color: theme.centerChannelColor,
diff --git a/share_extension/android/extension_post/extension_post.test.js b/share_extension/android/extension_post/extension_post.test.js
new file mode 100644
index 000000000..2422be80a
--- /dev/null
+++ b/share_extension/android/extension_post/extension_post.test.js
@@ -0,0 +1,76 @@
+// Copyright (c) 2015-present Mattermost, Inc. All Rights Reserved.
+// See LICENSE.txt for license information.
+
+import React from 'react';
+import {Alert, PermissionsAndroid} from 'react-native';
+import {shallowWithIntl} from 'test/intl-test-helper';
+
+import ExtensionPost from './extension_post';
+
+jest.spyOn(Alert, 'alert').mockReturnValue(true);
+jest.spyOn(PermissionsAndroid, 'check').mockReturnValue(PermissionsAndroid.RESULTS.GRANTED);
+
+jest.mock('react-navigation-stack/dist/views/TouchableItem', () => {});
+
+jest.mock('NativeModules', () => ({
+    MattermostShare: {
+        close: jest.fn(),
+    },
+    RNKeychainManager: {
+        SECURITY_LEVEL_ANY: 'ANY',
+    },
+}));
+
+jest.mock('app/mattermost_managed', () => ({
+    getConfig: jest.fn().mockReturnValue(false),
+}));
+
+const MAX_MESSAGE_LENGTH = 4000;
+
+describe('ExtensionPost', () => {
+    const baseProps = {
+        actions: {
+            getTeamChannels: jest.fn(),
+        },
+        channelId: 'channel-id',
+        channels: {},
+        currentUserId: 'current-user-id',
+        maxFileSize: 1024,
+        navigation: {
+            setParams: jest.fn(),
+        },
+        teamId: 'team-id',
+    };
+
+    const wrapper = shallowWithIntl(
+        <ExtensionPost {...baseProps}/>
+    );
+
+    const instance = wrapper.instance();
+
+    const postMessage = (message) => {
+        wrapper.setState({value: message});
+        instance.onPost();
+    };
+
+    test('should show Alert dialog if shared message is longer than maximum length permitted', () => {
+        const longMessage = 'a'.repeat(MAX_MESSAGE_LENGTH + 1);
+        postMessage(longMessage);
+
+        expect(Alert.alert).toHaveBeenCalledTimes(1);
+    });
+
+    test('should not show Alert dialog if shared message is within maximum length permitted', () => {
+        const message = 'a'.repeat(MAX_MESSAGE_LENGTH - 1);
+        postMessage(message);
+
+        expect(Alert.alert).not.toHaveBeenCalled();
+    });
+
+    test('should not show Alert dialog if shared message is at maximum length permitted', () => {
+        const exactLengthMessage = 'a'.repeat(MAX_MESSAGE_LENGTH);
+        postMessage(exactLengthMessage);
+
+        expect(Alert.alert).not.toHaveBeenCalled();
+    });
+});