diff --git a/lib/src/constants.dart b/lib/src/constants.dart
index a8c9ea4aa..8414488cf 100644
--- a/lib/src/constants.dart
+++ b/lib/src/constants.dart
@@ -8,12 +8,13 @@ import 'state/grid.dart';
 
 // WARNING: Do not modify line below, except for the version string
 //          (and also add new version string to scadnano_versions_to_link).
-const String CURRENT_VERSION = "0.17.4";
+const String CURRENT_VERSION = "0.17.5";
 const String INITIAL_VERSION = "0.1.0";
 
 // scadnano versions that we deploy so that older versions can be used.
 final scadnano_older_versions_to_link =[
   // "0.17.3", // accidentally skipped this version
+  "0.17.4",
   "0.17.2",
   "0.17.1",
   "0.17.0",
diff --git a/lib/src/middleware/helix_idxs_change.dart b/lib/src/middleware/helix_idxs_change.dart
index df531743f..1aa369ceb 100644
--- a/lib/src/middleware/helix_idxs_change.dart
+++ b/lib/src/middleware/helix_idxs_change.dart
@@ -12,6 +12,35 @@ helix_idxs_change_middleware(Store<AppState> store, dynamic action, NextDispatch
     Set<int> existing_idxs = store.state.design.helices.keys.toSet();
     Set<int> old_idxs = action.idx_replacements.keys.toSet();
     Set<int> remaining_idxs = existing_idxs.difference(old_idxs);
+    var new_indices = action.idx_replacements.values.toSet();
+
+    if (new_indices.length != action.idx_replacements.length) {
+      Map<int, List<int>> key_to_idxs = new Map<int, List<int>>();
+
+      for (var old_index in old_idxs) {
+        var new_index = action.idx_replacements[old_index];
+        if (key_to_idxs.containsKey(new_index))
+          key_to_idxs[new_index].add(old_index);
+        else
+          key_to_idxs[new_index] = [ old_index ];
+      }
+
+      if (key_to_idxs.length != action.idx_replacements.length) {
+        var msg = 'You tried to assign existing helices ';
+        
+        msg += key_to_idxs.entries.where((element) => element.value.length != 1).map((element) {
+          return element.value.join(', ') + " to " + element.key.toString();
+        }).join(" and helices ");
+
+        msg += ". Each helix must have a unique new index; make sure all the integers you write are distinct from each other and do not appear elsewhere in the design";
+
+        window.alert(msg);
+        return;
+      }
+
+
+    }
+
     for (int new_idx in action.idx_replacements.values) {
       if (remaining_idxs.contains(new_idx)) {
         var msg = 'Index ${new_idx} is already taken.';
diff --git a/lib/src/reducers/helices_reducer.dart b/lib/src/reducers/helices_reducer.dart
index ba037a75b..d09d3cad0 100644
--- a/lib/src/reducers/helices_reducer.dart
+++ b/lib/src/reducers/helices_reducer.dart
@@ -89,12 +89,13 @@ Design helix_idx_change_reducer(Design design, AppState state, actions.HelixIdxs
   var strands = design.strands.toList();
 
   Map<String, HelixGroup> new_groups = change_groups(action, helices, design);
-
+  var copy_helices = design.helices.toMap();
   // change helices
+
+  helices.removeWhere((key, _) => action.idx_replacements.containsKey(key));
   for (int old_idx in action.idx_replacements.keys) {
     int new_idx = action.idx_replacements[old_idx];
-    var helix = helices[old_idx].rebuild((b) => b..idx = new_idx);
-    helices.remove(old_idx);
+    var helix = copy_helices[old_idx].rebuild((b) => b..idx = new_idx);
     helices[new_idx] = helix;
   }
 
diff --git a/lib/src/serializers.dart b/lib/src/serializers.dart
index ef921efa7..e2a554dea 100644
--- a/lib/src/serializers.dart
+++ b/lib/src/serializers.dart
@@ -288,6 +288,7 @@ part 'serializers.g.dart';
   DialogShow,
   DialogHide,
   DialogLink,
+  DialogLabel,
   StrandOrder,
   StrandColorSet,
   StrandColorPickerShow,
diff --git a/lib/src/state/dialog.dart b/lib/src/state/dialog.dart
index 1fc637567..d633e31f5 100644
--- a/lib/src/state/dialog.dart
+++ b/lib/src/state/dialog.dart
@@ -305,6 +305,8 @@ abstract class DialogLink
       ..tooltip = tooltip);
   }
 
+
+
   /************************ end BuiltValue boilerplate ************************/
 
   String get label;
@@ -314,6 +316,33 @@ abstract class DialogLink
   String get value;
 }
 
+abstract class DialogLabel
+    with BuiltJsonSerializable
+    implements DialogItem, Built<DialogLabel, DialogLabelBuilder> {
+  DialogLabel._();
+
+  factory DialogLabel.from([void Function(DialogLabelBuilder) updates]) = _$DialogLabel;
+
+  static Serializer<DialogLabel> get serializer => _$dialogLabelSerializer;
+
+  @memoized
+  int get hashCode;
+
+  factory DialogLabel({String label, String tooltip}) {
+    return DialogLabel.from((b) => b
+      ..label = label
+      ..value = ""
+      ..tooltip = tooltip);
+  }
+
+
+  /************************ end BuiltValue boilerplate ************************/
+
+  String get label;
+
+  String get value;
+}
+
 // abstract class DialogLink
 //     with BuiltJsonSerializable
 //     implements DialogItem, Built<DialogLink, DialogLinkBuilder> {
diff --git a/lib/src/view/design_dialog_form.dart b/lib/src/view/design_dialog_form.dart
index 1fa764399..cfddd9b44 100644
--- a/lib/src/view/design_dialog_form.dart
+++ b/lib/src/view/design_dialog_form.dart
@@ -318,6 +318,13 @@ class DesignDialogFormComponent extends UiStatefulComponent2<DesignDialogFormPro
         ..href = item.link
         ..target = '_blank')(item.label);
     }
+    else if (item is DialogLabel) {
+      return (Dom.span()
+        ..title = item.tooltip
+        )(item.label);
+    }
+
+
     return null;
   }
 
diff --git a/lib/src/view/design_main_error_boundary.dart b/lib/src/view/design_main_error_boundary.dart
index 1ff4fa83a..199cf426b 100644
--- a/lib/src/view/design_main_error_boundary.dart
+++ b/lib/src/view/design_main_error_boundary.dart
@@ -120,5 +120,6 @@ class DesignMainErrorBoundaryComponent<T extends DesignMainErrorBoundaryProps,
 
 send_error(String escaped_error_message) async{
   app.dispatch(actions.ErrorMessageSet(escaped_error_message));
+  app.dispatch(actions.LoadingDialogHide());    // close loading dialog if it's currently being shown
   app.view.design_view.render(app.state);
 }
diff --git a/lib/src/view/menu_side.dart b/lib/src/view/menu_side.dart
index 81c8714fa..896aa7c7a 100644
--- a/lib/src/view/menu_side.dart
+++ b/lib/src/view/menu_side.dart
@@ -96,6 +96,11 @@ class SideMenuComponent extends UiComponent2<SideMenuProps> with RedrawCounterMi
         ..disabled = props.groups.length == 1
         ..on_click = ((ev) => app.dispatch(actions.GroupRemove(name: props.displayed_group_name)))
         ..key = 'remove-current-group')(),
+      (MenuDropdownItem()
+        ..display = 'adjust helix indices'
+        ..disabled = props.groups[props.displayed_group_name].helices_view_order.length == 0
+        ..on_click = ((ev) => adjust_helix_indices_for_current_group())
+        ..key = 'adjust-helix-indices')(),
     ]);
     return NavDropdown({
       'title': 'Group',
@@ -125,6 +130,9 @@ class SideMenuComponent extends UiComponent2<SideMenuProps> with RedrawCounterMi
   set_new_parameters_for_current_group() =>
       app.disable_keyboard_shortcuts_while(ask_new_parameters_for_current_group);
 
+  adjust_helix_indices_for_current_group() =>
+    app.disable_keyboard_shortcuts_while(ask_new_helix_indices_for_current_group);
+
   add_new_group(Iterable<String> existing_names) =>
       app.disable_keyboard_shortcuts_while(() => ask_about_new_group(existing_names));
 
@@ -262,4 +270,31 @@ class SideMenuComponent extends UiComponent2<SideMenuProps> with RedrawCounterMi
     app.dispatch(
         actions.GroupChange(old_name: props.displayed_group_name, new_name: new_name, new_group: new_group));
   }
+
+  Future<void> ask_new_helix_indices_for_current_group() async {
+    var group = props.groups[props.displayed_group_name];
+    var existing_grid = group.grid;
+
+    List<DialogItem> items = []; 
+    items.add(DialogLabel(label: 'current view order: ' + group.helices_view_order.join(' ')));
+
+    for (var helix_index in group.helices_view_order) {
+      items.add(DialogInteger(label: helix_index.toString(), value: helix_index));
+    }
+
+    var dialog =
+        Dialog(title: 'adjust Helix indices', items: items);
+    List<DialogItem> results = await util.dialog(dialog);
+    if (results == null) return;
+
+    Map<int, int> new_indices_map = {}; 
+    for (int i = 1; i < results.length; i++) {
+      new_indices_map[group.helices_view_order[i-1]] = (results[i] as DialogInteger).value; 
+    }
+
+   app.dispatch(actions.HelixIdxsChange(idx_replacements: new_indices_map));
+  }
+
 }
+
+
diff --git a/web/scadnano-styles.css b/web/scadnano-styles.css
index 8f86f8a2c..bf0c3b09f 100644
--- a/web/scadnano-styles.css
+++ b/web/scadnano-styles.css
@@ -1,5 +1,5 @@
-
-html, body {
+html,
+body {
     width: 100%;
     height: 100%;
     margin: 0;
@@ -11,12 +11,14 @@ html, body {
 ** BEGIN layout
 ************************************************/
 
-input[type = checkbox] {
+input[type=checkbox] {
     margin-right: 4px;
 }
-label + select {
+
+label+select {
     margin-left: 4px;
 }
+
 .radio-left {
     text-align: left;
 }
@@ -65,7 +67,7 @@ label + select {
 #design-and-modes-buttons-container {
     display: flex;
     height: 100%;
-    width: 100%; 
+    width: 100%;
     overflow: hidden;
 }
 
@@ -99,7 +101,8 @@ label + select {
     position: relative;
 }
 
-#side-arrows, #main-arrows {
+#side-arrows,
+#main-arrows {
     position: absolute;
     left: 0;
     bottom: 0;
@@ -108,11 +111,11 @@ label + select {
     filter: drop-shadow(0px 0px 5px rgb(255 255 255));
 }
 
-.arrow-group{
+.arrow-group {
     pointer-events: bounding-box;
 }
 
-.axis-arrow{
+.axis-arrow {
     stroke-width: 3;
     stroke-linecap: round;
 }
@@ -153,7 +156,8 @@ label + select {
     padding-right: 5px;
 }
 
-.dialog-form-container, .dialog-loading-container {
+.dialog-form-container,
+.dialog-loading-container {
     position: fixed;
     top: 50%;
     left: 50%;
@@ -170,6 +174,8 @@ label + select {
     border: 1px solid #B2B2B2;
     background: #F9F9F9;
     box-shadow: 3px 3px 2px #E9E9E9;
+    max-height: 80vh;
+    overflow-y: auto;
 }
 
 .dialog-form-item {
@@ -205,7 +211,7 @@ label + select {
     font-style: italic;
 }
 
-.dialog-design-loading span {    
+.dialog-design-loading span {
     animation: pulse 0.8s infinite alternate;
 }
 
@@ -261,7 +267,7 @@ label + select {
     top: 0;
 }
 
-.has-submenu:hover > .context-menu {
+.has-submenu:hover>.context-menu {
     visibility: visible;
 }
 
@@ -277,7 +283,7 @@ label + select {
     pointer-events: none;
 }
 
-.has-submenu > .context-menu-item::after {
+.has-submenu>.context-menu-item::after {
     content: '';
     position: absolute;
     top: 50%;
@@ -290,7 +296,7 @@ label + select {
 }
 
 .context-menu-item:hover,
-.has-submenu:hover > .context-menu-item {
+.has-submenu:hover>.context-menu-item {
     color: white;
     background: #284570;
     border-radius: 2px;
@@ -315,6 +321,7 @@ label + select {
     background: #F9F9F9 !important;
     box-shadow: none !important;
 }
+
 /*.panes-container {*/
 /*  display: flex;*/
 /*  width: 100%;*/
@@ -413,7 +420,7 @@ label + select {
     width: 100%;
 }
 
-.edit-mode-toggle-button{
+.edit-mode-toggle-button {
     position: absolute;
     width: 25px;
     bottom: 24px;
@@ -421,11 +428,11 @@ label + select {
     right: calc(100% + 20px);
 }
 
-.edit-mode-toggle-button img.appear{
+.edit-mode-toggle-button img.appear {
     transform: rotate(180deg);
 }
 
-.edit-mode-toggle-button img{
+.edit-mode-toggle-button img {
     pointer-events: none;
     max-width: 100%;
 
@@ -444,7 +451,8 @@ label + select {
     padding: 5px 10px;
     border-top: 1px solid black;
 }
-.mode-button>img{
+
+.mode-button>img {
     width: 25px;
     pointer-events: none;
 }
@@ -504,11 +512,16 @@ label + select {
 
 /* show open hand when cursor is over SVG background itself */
 .panzoomable {
-    cursor: move; /* fallback: no `url()` support or images disabled */
-    cursor: url(images/grab.png), auto; /* fallback: Internet Explorer */
-    cursor: -webkit-grab; /* Chrome 1-21, Safari 4+ */
-    cursor: -moz-grab; /* Firefox 1.5-26 */
-    cursor: grab; /* W3C standards syntax, should come least */
+    cursor: move;
+    /* fallback: no `url()` support or images disabled */
+    cursor: url(images/grab.png), auto;
+    /* fallback: Internet Explorer */
+    cursor: -webkit-grab;
+    /* Chrome 1-21, Safari 4+ */
+    cursor: -moz-grab;
+    /* Firefox 1.5-26 */
+    cursor: grab;
+    /* W3C standards syntax, should come least */
 }
 
 /* show regular cursor arrow when cursor is over an element in the SVG, not the SVG background itself */
@@ -528,11 +541,13 @@ label + select {
     cursor: crosshair;
 }
 
-.domain-name-text, .strand-name-text {
+.domain-name-text,
+.strand-name-text {
     text-anchor: middle;
 }
 
-.selection-box,.selection-rope {
+.selection-box,
+.selection-rope {
     stroke: dimgray;
     fill: gray;
     fill-opacity: 0.5;
@@ -569,11 +584,13 @@ label + select {
     stroke: #B0B0B0;
 }
 
-.helix-horz-line, .helix-vert-minor-line {
+.helix-horz-line,
+.helix-vert-minor-line {
     stroke-width: 0.5;
 }
 
-.helix-vert-end-line, .helix-vert-major-line {
+.helix-vert-end-line,
+.helix-vert-major-line {
     stroke-width: 3;
 }
 
@@ -591,7 +608,8 @@ label + select {
     stroke: black;
     stroke-width: 0.5px;
     fill-opacity: 0.5;
-    pointer-events: none; /* XXX: need this so we can detect mouse up on non-moving end underneath */
+    pointer-events: none;
+    /* XXX: need this so we can detect mouse up on non-moving end underneath */
 }
 
 .five-prime-end,
@@ -649,6 +667,7 @@ https://stackoverflow.com/questions/47758565/adding-fedropshadow-to-a-vertical-l
     stroke: hotpink;
     stroke-width: 5pt;
 }
+
 .selected.five-prime-end,
 .selected.three-prime-end,
 .selected.five-prime-end-first-substrand,
@@ -672,6 +691,7 @@ https://stackoverflow.com/questions/47758565/adding-fedropshadow-to-a-vertical-l
     stroke: hotpink;
     stroke-width: 5pt;
 }
+
 .selected .five-prime-end,
 .selected .three-prime-end,
 .selected .five-prime-end-first-substrand,
@@ -751,10 +771,15 @@ https://stackoverflow.com/questions/47758565/adding-fedropshadow-to-a-vertical-l
 .modification-text {
     text-anchor: middle;
     font-weight: bold;
-    text-shadow: /*-1px -1px 0 #fff,*/ /*1px -1px 0 #fff,*/ /*-1px 1px 0 #fff,*/ /*1px 1px 0 #fff;*/ -0.7px -0.7px 0 #fff,
-    0.7px -0.7px 0 #fff,
-    -0.7px 0.7px 0 #fff,
-    0.7px 0.7px 0 #fff;
+    text-shadow:
+        /*-1px -1px 0 #fff,*/
+        /*1px -1px 0 #fff,*/
+        /*-1px 1px 0 #fff,*/
+        /*1px 1px 0 #fff;*/
+        -0.7px -0.7px 0 #fff,
+        0.7px -0.7px 0 #fff,
+        -0.7px 0.7px 0 #fff,
+        0.7px 0.7px 0 #fff;
 }
 
 .dna-seq {
@@ -764,12 +789,19 @@ https://stackoverflow.com/questions/47758565/adding-fedropshadow-to-a-vertical-l
     text-anchor: start;
     pointer-events: none;
     dominant-baseline: ideographic;
-    text-shadow: /*-1px -1px 0 #fff,*/ /*1px -1px 0 #fff,*/ /*-1px 1px 0 #fff,*/ /*1px 1px 0 #fff;*/ -0.7px -0.7px 0 #fff,
-    0.7px -0.7px 0 #fff,
-    -0.7px 0.7px 0 #fff,
-    0.7px 0.7px 0 #fff;
-    text-rendering: optimizeSpeed; /* doesn't seem to do much to improve rendering speed */
-    white-space: pre; /* needed to display multiple space symbols in a row */
+    text-shadow:
+        /*-1px -1px 0 #fff,*/
+        /*1px -1px 0 #fff,*/
+        /*-1px 1px 0 #fff,*/
+        /*1px 1px 0 #fff;*/
+        -0.7px -0.7px 0 #fff,
+        0.7px -0.7px 0 #fff,
+        -0.7px 0.7px 0 #fff,
+        0.7px 0.7px 0 #fff;
+    text-rendering: optimizeSpeed;
+    /* doesn't seem to do much to improve rendering speed */
+    white-space: pre;
+    /* needed to display multiple space symbols in a row */
 }
 
 .loopout-extension-length,
@@ -780,10 +812,11 @@ https://stackoverflow.com/questions/47758565/adding-fedropshadow-to-a-vertical-l
     font-weight: bold;
     text-anchor: middle;
     pointer-events: none;
-    text-shadow: /*-1px -1px 0 #fff,*/ /*1px -1px 0 #fff,*/ /*-1px 1px 0 #fff,*/ /*1px 1px 0 #fff;*/ -0.7px -0.7px 0 #fff,
-    0.7px -0.7px 0 #fff,
-    -0.7px 0.7px 0 #fff,
-    0.7px 0.7px 0 #fff;
+    text-shadow:
+        -0.7px -0.7px 0 #fff,
+        0.7px -0.7px 0 #fff,
+        -0.7px 0.7px 0 #fff,
+        0.7px 0.7px 0 #fff;
     text-rendering: optimizeSpeed; /* doesn't seem to do much to improve rendering speed */
     white-space: pre; /* needed to display multiple space symbols in a row */
 }
@@ -802,12 +835,19 @@ https://stackoverflow.com/questions/47758565/adding-fedropshadow-to-a-vertical-l
     text-anchor: middle;
     pointer-events: none;
     dominant-baseline: ideographic;
-    text-shadow: /*-1px -1px 0 #fff,*/ /*1px -1px 0 #fff,*/ /*-1px 1px 0 #fff,*/ /*1px 1px 0 #fff;*/ -0.7px -0.7px 0 #fff,
-    0.7px -0.7px 0 #fff,
-    -0.7px 0.7px 0 #fff,
-    0.7px 0.7px 0 #fff;
-    text-rendering: optimizeSpeed; /* doesn't seem to do much to improve rendering speed */
-    white-space: pre; /* needed to display multiple space symbols in a row */
+    text-shadow:
+        /*-1px -1px 0 #fff,*/
+        /*1px -1px 0 #fff,*/
+        /*-1px 1px 0 #fff,*/
+        /*1px 1px 0 #fff;*/
+        -0.7px -0.7px 0 #fff,
+        0.7px -0.7px 0 #fff,
+        -0.7px 0.7px 0 #fff,
+        0.7px 0.7px 0 #fff;
+    text-rendering: optimizeSpeed;
+    /* doesn't seem to do much to improve rendering speed */
+    white-space: pre;
+    /* needed to display multiple space symbols in a row */
 }
 
 /* next is needed so that we can rotate ends on extensions
@@ -842,7 +882,8 @@ https://stackoverflow.com/questions/15138801/rotate-rectangle-around-its-own-cen
     font-family: Helvetica, serif;
     font-size: 32pt;
     fill: DarkBlue;
-    stroke: none; /* don't know why this is necessary to prevent a gray stoke from hiding most of the text */
+    stroke: none;
+    /* don't know why this is necessary to prevent a gray stoke from hiding most of the text */
     text-anchor: middle;
     dominant-baseline: central;
 }
@@ -866,7 +907,9 @@ https://stackoverflow.com/questions/15138801/rotate-rectangle-around-its-own-cen
 ************************************************/
 
 /* Thin the navbar */
-.navbar, .dropdown-menu, .form-control {
+.navbar,
+.dropdown-menu,
+.form-control {
     font-size: 0.8rem;
 }
 
@@ -891,12 +934,12 @@ https://stackoverflow.com/questions/15138801/rotate-rectangle-around-its-own-cen
 }
 
 /* File checkmarks appear on one line */
-#file-nav-dropdown + .dropdown-menu label {
+#file-nav-dropdown+.dropdown-menu label {
     white-space: nowrap;
 }
 
 /* View checkmarks appear on one line */
-#view-nav-dropdown + .dropdown-menu label {
+#view-nav-dropdown+.dropdown-menu label {
     white-space: nowrap;
 }
 
@@ -954,7 +997,8 @@ https://stackoverflow.com/questions/15138801/rotate-rectangle-around-its-own-cen
 ************************************************/
 
 /* Style dropdown item of selected grid as well as newly clicked on grid */
-#grid-nav-dropdown + .dropdown-menu .dropdown-item.disabled, .dropdown-item:active {
+#grid-nav-dropdown+.dropdown-menu .dropdown-item.disabled,
+.dropdown-item:active {
     color: #fff;
     text-decoration: none;
     background-color: #686868;
@@ -966,11 +1010,12 @@ https://stackoverflow.com/questions/15138801/rotate-rectangle-around-its-own-cen
 }
 
 /* Styles the label like a DropdownItem */
-.form-file-dropdown .custom-file-input + .custom-file-label {
+.form-file-dropdown .custom-file-input+.custom-file-label {
     display: block;
     width: 100%;
     padding: .25rem 1.5rem;
-    margin-bottom: 0%; /* Removes label browser default */
+    margin-bottom: 0%;
+    /* Removes label browser default */
     clear: both;
     font-weight: 400;
     color: #212529;
@@ -981,14 +1026,14 @@ https://stackoverflow.com/questions/15138801/rotate-rectangle-around-its-own-cen
 }
 
 /* Styles the label like a DropdownItem (on hover) */
-.form-file-dropdown .custom-file-input + .custom-file-label:hover {
+.form-file-dropdown .custom-file-input+.custom-file-label:hover {
     color: #16181b;
     text-decoration: none;
     background-color: #f8f9fa;
 }
 
 /* Hides the data-browse psuedo-element. */
-.form-file-dropdown .custom-file-input + .custom-file-label::after {
+.form-file-dropdown .custom-file-input+.custom-file-label::after {
     content: none;
 }
 
@@ -1007,7 +1052,7 @@ https://stackoverflow.com/questions/15138801/rotate-rectangle-around-its-own-cen
 ************************************************/
 
 .slice-bar-rect rect {
-    fill:goldenrod;
+    fill: goldenrod;
     fill-opacity: 50%;
     cursor: move;
     stroke: rgb(131, 97, 3);
@@ -1015,7 +1060,7 @@ https://stackoverflow.com/questions/15138801/rotate-rectangle-around-its-own-cen
 }
 
 .slice-bar-rect text {
-    fill:rgb(131, 97, 3);
+    fill: rgb(131, 97, 3);
     fill-opacity: 100%;
     font-size: 12px;
     text-anchor: middle;