diff --git a/app/soapbox/actions/__tests__/compose.test.js b/app/soapbox/actions/__tests__/compose.test.js
new file mode 100644
index 000000000..ec20acf0f
--- /dev/null
+++ b/app/soapbox/actions/__tests__/compose.test.js
@@ -0,0 +1,103 @@
+import { InstanceRecord } from 'soapbox/normalizers';
+import rootReducer from 'soapbox/reducers';
+import { mockStore } from 'soapbox/test_helpers';
+
+import { uploadCompose } from '../compose';
+
+describe('uploadCompose()', () => {
+  describe('with images', () => {
+    let files, store;
+
+    beforeEach(() => {
+      const instance = InstanceRecord({
+        configuration: {
+          statuses: {
+            max_media_attachments: 4,
+          },
+          media_attachments: {
+            image_size_limit: 10,
+          },
+        },
+      });
+
+      const state = rootReducer(undefined, {})
+        .set('me', '1234')
+        .set('instance', instance);
+
+      store = mockStore(state);
+      files = [{
+        uri: 'image.png',
+        name: 'Image',
+        size: 15,
+        type: 'image/png',
+      }];
+    });
+
+    it('creates an alert if exceeds max size', async() => {
+      const expectedActions = [
+        { type: 'COMPOSE_UPLOAD_REQUEST', skipLoading: true },
+        {
+          type: 'ALERT_SHOW',
+          message: 'Image exceeds the current file size limit (10 Bytes)',
+          actionLabel: undefined,
+          actionLink: undefined,
+          severity: 'error',
+        },
+        { type: 'COMPOSE_UPLOAD_FAIL', error: true, skipLoading: true },
+      ];
+
+      await store.dispatch(uploadCompose(files));
+      const actions = store.getActions();
+
+      expect(actions).toEqual(expectedActions);
+    });
+  });
+
+  describe('with videos', () => {
+    let files, store;
+
+    beforeEach(() => {
+      const instance = InstanceRecord({
+        configuration: {
+          statuses: {
+            max_media_attachments: 4,
+          },
+          media_attachments: {
+            video_size_limit: 10,
+          },
+        },
+      });
+
+      const state = rootReducer(undefined, {})
+        .set('me', '1234')
+        .set('instance', instance);
+
+      store = mockStore(state);
+      files = [{
+        uri: 'video.mp4',
+        name: 'Video',
+        size: 15,
+        type: 'video/mp4',
+      }];
+    });
+
+    it('creates an alert if exceeds max size', async() => {
+      const expectedActions = [
+        { type: 'COMPOSE_UPLOAD_REQUEST', skipLoading: true },
+        {
+          type: 'ALERT_SHOW',
+          message: 'Video exceeds the current file size limit (10 Bytes)',
+          actionLabel: undefined,
+          actionLink: undefined,
+          severity: 'error',
+        },
+        { type: 'COMPOSE_UPLOAD_FAIL', error: true, skipLoading: true },
+      ];
+
+      await store.dispatch(uploadCompose(files));
+      const actions = store.getActions();
+
+      expect(actions).toEqual(expectedActions);
+    });
+  });
+});
diff --git a/app/soapbox/actions/compose.js b/app/soapbox/actions/compose.js
index 25e5fa4f1..3cebf8459 100644
--- a/app/soapbox/actions/compose.js
+++ b/app/soapbox/actions/compose.js
@@ -6,6 +6,7 @@ import { defineMessages } from 'react-intl';
 import snackbar from 'soapbox/actions/snackbar';
 import { isLoggedIn } from 'soapbox/utils/auth';
 import { getFeatures } from 'soapbox/utils/features';
+import { formatBytes } from 'soapbox/utils/media';
 
 import api from '../api';
 import { search as emojiSearch } from '../features/emoji/emoji_mart_search_light';
@@ -299,6 +300,8 @@ export function uploadCompose(files) {
   return function(dispatch, getState) {
     if (!isLoggedIn(getState)) return;
     const attachmentLimit = getState().getIn(['instance', 'configuration', 'statuses', 'max_media_attachments']);
+    const maxImageSize = getState().getIn(['instance', 'configuration', 'media_attachments', 'image_size_limit']);
+    const maxVideoSize = getState().getIn(['instance', 'configuration', 'media_attachments', 'video_size_limit']);
 
     const media  = getState().getIn(['compose', 'media_attachments']);
     const progress = new Array(files.length).fill(0);
@@ -314,6 +317,20 @@ export function uploadCompose(files) {
     Array.from(files).forEach((f, i) => {
       if (media.size + i > attachmentLimit - 1) return;
 
+      const isImage = f.type.match(/image.*/);
+      const isVideo = f.type.match(/video.*/);
+      if (isImage && maxImageSize && (f.size > maxImageSize)) {
+        const message = `Image exceeds the current file size limit (${formatBytes(maxImageSize)})`;
+        dispatch(snackbar.error(message));
+        dispatch(uploadComposeFail(true));
+        return;
+      } else if (isVideo && maxVideoSize && (f.size > maxVideoSize)) {
+        const message = `Video exceeds the current file size limit (${formatBytes(maxVideoSize)})`;
+        dispatch(snackbar.error(message));
+        dispatch(uploadComposeFail(true));
+        return;
+      }
+
       // FIXME: Don't define function in loop
       /* eslint-disable no-loop-func */
       resizeImage(f).then(file => {
diff --git a/app/soapbox/utils/media.ts b/app/soapbox/utils/media.ts
index c8266c646..74fc4d3f8 100644
--- a/app/soapbox/utils/media.ts
+++ b/app/soapbox/utils/media.ts
@@ -1,6 +1,10 @@
-export const truncateFilename = (url, maxLength) => {
+const truncateFilename = (url: string, maxLength: number) => {
   const filename = url.split('/').pop();
 
+  if (!filename) {
+    return filename;
+  }
+
   if (filename.length <= maxLength) return filename;
 
   return [
@@ -8,3 +12,17 @@ export const truncateFilename = (url, maxLength) => {
     filename.substr(filename.length - maxLength/2),
   ].join('…');
 };
+
+const formatBytes = (bytes: number, decimals: number = 2) => {
+  if (bytes === 0) return '0 Bytes';
+
+  const k = 1024;
+  const dm = decimals < 0 ? 0 : decimals;
+  const sizes = ['Bytes', 'KB', 'MB', 'GB', 'TB', 'PB', 'EB', 'ZB', 'YB'];
+
+  const i = Math.floor(Math.log(bytes) / Math.log(k));
+
+  return parseFloat((bytes / Math.pow(k, i)).toFixed(dm)) + ' ' + sizes[i];
+};
+
+export { formatBytes, truncateFilename };