diff --git a/app/assets/javascripts/discourse/components/composer-editor.js.es6 b/app/assets/javascripts/discourse/components/composer-editor.js.es6
index 9f06d80b7f7..2c6e4ea6404 100644
--- a/app/assets/javascripts/discourse/components/composer-editor.js.es6
+++ b/app/assets/javascripts/discourse/components/composer-editor.js.es6
@@ -493,7 +493,7 @@ export default Ember.Component.extend({
       this._xhr = null;
 
       if (!userCancelled) {
-        displayErrorForUpload(data.jqXHR.responseJSON);
+        displayErrorForUpload(data);
       }
     });
 
diff --git a/app/assets/javascripts/discourse/lib/utilities.js.es6 b/app/assets/javascripts/discourse/lib/utilities.js.es6
index dde738d9a83..33558befacb 100644
--- a/app/assets/javascripts/discourse/lib/utilities.js.es6
+++ b/app/assets/javascripts/discourse/lib/utilities.js.es6
@@ -334,27 +334,27 @@ export function getUploadMarkdown(upload) {
 }
 
 export function displayErrorForUpload(data) {
-  // deal with meaningful errors first
   if (data.jqXHR) {
     switch (data.jqXHR.status) {
       // cancelled by the user
-      case 0: return;
+      case 0:
+        return;
 
-              // entity too large, usually returned from the web server
+      // entity too large, usually returned from the web server
       case 413:
-              var type = uploadTypeFromFileName(data.files[0].name);
-              var maxSizeKB = Discourse.SiteSettings['max_' + type + '_size_kb'];
-              bootbox.alert(I18n.t('post.errors.file_too_large', { max_size_kb: maxSizeKB }));
-              return;
+        const type = uploadTypeFromFileName(data.files[0].name);
+        const max_size_kb = Discourse.SiteSettings[`max_${type}_size_kb`];
+        bootbox.alert(I18n.t('post.errors.file_too_large', { max_size_kb }));
+        return;
 
-              // the error message is provided by the server
+      // the error message is provided by the server
       case 422:
-              if (data.jqXHR.responseJSON.message) {
-                bootbox.alert(data.jqXHR.responseJSON.message);
-              } else {
-                bootbox.alert(data.jqXHR.responseJSON.join("\n"));
-              }
-              return;
+        if (data.jqXHR.responseJSON.message) {
+          bootbox.alert(data.jqXHR.responseJSON.message);
+        } else {
+          bootbox.alert(data.jqXHR.responseJSON.join("\n"));
+        }
+        return;
     }
   } else if (data.errors && data.errors.length > 0) {
     bootbox.alert(data.errors.join("\n"));
diff --git a/app/assets/javascripts/discourse/mixins/upload.js.es6 b/app/assets/javascripts/discourse/mixins/upload.js.es6
index 1dc55eeb851..eec73d8c3d1 100644
--- a/app/assets/javascripts/discourse/mixins/upload.js.es6
+++ b/app/assets/javascripts/discourse/mixins/upload.js.es6
@@ -56,7 +56,7 @@ export default Em.Mixin.create({
     });
 
     $upload.on("fileuploadfail", (e, data) => {
-      displayErrorForUpload(data.jqXHR.responseJSON);
+      displayErrorForUpload(data);
       reset();
     });
   }.on("didInsertElement"),
diff --git a/app/controllers/uploads_controller.rb b/app/controllers/uploads_controller.rb
index 8ea6c766eb2..dcfaa4ed3c5 100644
--- a/app/controllers/uploads_controller.rb
+++ b/app/controllers/uploads_controller.rb
@@ -26,17 +26,22 @@ class UploadsController < ApplicationController
     # note, atm hijack is processed in its own context and has not access to controller
     # longer term we may change this
     hijack do
-      info = UploadsController.create_upload(
-        current_user: me,
-        file: file,
-        url: url,
-        type: type,
-        for_private_message: for_private_message,
-        pasted: pasted,
-        is_api: is_api,
-        retain_hours: retain_hours
-      )
-      render json: UploadsController.serialize_upload(info), status: Upload === info ? 200 : 422
+      begin
+        info = UploadsController.create_upload(
+          current_user: me,
+          file: file,
+          url: url,
+          type: type,
+          for_private_message: for_private_message,
+          pasted: pasted,
+          is_api: is_api,
+          retain_hours: retain_hours
+        )
+      rescue => e
+        render json: failed_json.merge(message: e.message&.split("\n")&.first), status: 422
+      else
+        render json: UploadsController.serialize_upload(info), status: Upload === info ? 200 : 422
+      end
     end
   end
 
diff --git a/config/locales/server.en.yml b/config/locales/server.en.yml
index a44704fd897..9d2ce6e56f3 100644
--- a/config/locales/server.en.yml
+++ b/config/locales/server.en.yml
@@ -2873,6 +2873,7 @@ en:
     store_failure: "Failed to store upload #%{upload_id} for user #%{user_id}."
     file_missing: "Sorry, you must provide a file to upload."
     empty: "Sorry, but the file you provided is empty."
+    png_to_jpg_conversion_failure_message: "An error happened when converting from PNG to JPG."
     attachments:
       too_large: "Sorry, the file you are trying to upload is too big (maximum size is %{max_size_kb}KB)."
     images:
diff --git a/lib/upload_creator.rb b/lib/upload_creator.rb
index 75f4b3cff6e..71057483203 100644
--- a/lib/upload_creator.rb
+++ b/lib/upload_creator.rb
@@ -163,7 +163,7 @@ class UploadCreator
     command << '-debug' << 'all' if debug
     command << output_file.path
 
-    Discourse::Utils.execute_command(*command, failure_message: "failed to convert png to jpg")
+    Discourse::Utils.execute_command(*command, failure_message: I18n.t("upload.png_to_jpg_conversion_failure_message"))
   end
 
   def should_downsize?