diff --git a/client/galaxy/scripts/mvc/upload/composite/composite-view.js b/client/galaxy/scripts/mvc/upload/composite/composite-view.js
index 8b12e2883a7..53fcfe02e6e 100644
--- a/client/galaxy/scripts/mvc/upload/composite/composite-view.js
+++ b/client/galaxy/scripts/mvc/upload/composite/composite-view.js
@@ -50,7 +50,8 @@ export default Backbone.View.extend({
                     _.each(details.composite_files, item => {
                         self.collection.add({
                             id: self.collection.size(),
-                            file_desc: item.description || item.name
+                            file_desc: item.description || item.name,
+                            optional: item.optional,
                         });
                     });
                 }
@@ -100,7 +101,7 @@ export default Backbone.View.extend({
             this.select_genome.enable();
             this.select_extension.enable();
         }
-        if (this.collection.where({ status: "ready" }).length == this.collection.length && this.collection.length > 0) {
+        if (this.collection.where({ status: "ready" }).length + this.collection.where({ optional: true }).length == this.collection.length && this.collection.length > 0) {
             this.btnStart.enable();
             this.btnStart.$el.addClass("btn-primary");
         } else {
diff --git a/client/galaxy/scripts/mvc/upload/upload-model.js b/client/galaxy/scripts/mvc/upload/upload-model.js
index 6a51f38c69b..3cb4c0d56fc 100644
--- a/client/galaxy/scripts/mvc/upload/upload-model.js
+++ b/client/galaxy/scripts/mvc/upload/upload-model.js
@@ -4,6 +4,7 @@ var Model = Backbone.Model.extend({
         genome: "?",
         url_paste: "",
         status: "init",
+        optional: false,
         info: null,
         file_name: "",
         file_mode: "",
diff --git a/client/galaxy/scripts/mvc/upload/upload-view.js b/client/galaxy/scripts/mvc/upload/upload-view.js
index 9c54c6886b3..eff6a242554 100644
--- a/client/galaxy/scripts/mvc/upload/upload-view.js
+++ b/client/galaxy/scripts/mvc/upload/upload-view.js
@@ -172,6 +172,8 @@ export default Backbone.View.extend({
                                 file: it.get("file_data")
                             });
                     }
+                } else if (it.get("optional")) {
+                    continue;
                 } else {
                     data.error_message = "Upload content incomplete.";
                     it.set("status", "error");