diff --git a/source/blender/editors/interface/interface.cc b/source/blender/editors/interface/interface.cc
index 8134aaa28c6..a7c7eebdbdb 100644
--- a/source/blender/editors/interface/interface.cc
+++ b/source/blender/editors/interface/interface.cc
@@ -906,6 +906,12 @@ static void ui_but_update_old_active_from_new(uiBut *oldbut, uiBut *but)
       progress_oldbut->progress_factor = progress_but->progress_factor;
       break;
     }
+    case UI_BTYPE_SEPR_LINE: {
+      uiButSeparatorLine *line_oldbut = (uiButSeparatorLine *)oldbut;
+      uiButSeparatorLine *line_but = (uiButSeparatorLine *)but;
+      line_oldbut->is_vertical = line_but->is_vertical;
+      break;
+    }
     case UI_BTYPE_VIEW_ITEM: {
       uiButViewItem *view_item_oldbut = (uiButViewItem *)oldbut;
       uiButViewItem *view_item_newbut = (uiButViewItem *)but;
@@ -3938,6 +3944,9 @@ static uiBut *ui_but_new(const eButType type)
     case UI_BTYPE_PROGRESS:
       but = MEM_new<uiButProgress>("uiButProgress");
       break;
+    case UI_BTYPE_SEPR_LINE:
+      but = MEM_new<uiButSeparatorLine>("uiButSeparatorLine");
+      break;
     case UI_BTYPE_HSVCUBE:
       but = MEM_new<uiButHSVCube>("uiButHSVCube");
       break;
diff --git a/source/blender/editors/interface/interface_intern.hh b/source/blender/editors/interface/interface_intern.hh
index 932b24b7f03..d68ed4560e1 100644
--- a/source/blender/editors/interface/interface_intern.hh
+++ b/source/blender/editors/interface/interface_intern.hh
@@ -389,6 +389,11 @@ struct uiButProgress : public uiBut {
   eButProgressType progress_type = UI_BUT_PROGRESS_TYPE_BAR;
 };
 
+/** Derived struct for #UI_BTYPE_SEPR_LINE. */
+struct uiButSeparatorLine : public uiBut {
+  bool is_vertical;
+};
+
 struct uiButViewItem : public uiBut {
   /* C-Handle to the view item this button was created for. */
   uiViewItemHandle *view_item = nullptr;
diff --git a/source/blender/editors/interface/interface_layout.cc b/source/blender/editors/interface/interface_layout.cc
index 7cc06a4bb6c..d02bcc2d2d1 100644
--- a/source/blender/editors/interface/interface_layout.cc
+++ b/source/blender/editors/interface/interface_layout.cc
@@ -3452,20 +3452,25 @@ void uiItemS_ex(uiLayout *layout, float factor, const LayoutSeparatorType type)
   bool is_vertical_bar = (layout->w == 0) && but_type == UI_BTYPE_SEPR_LINE;
 
   UI_block_layout_set_current(block, layout);
-  uiDefBut(block,
-           but_type,
-           0,
-           "",
-           0,
-           0,
-           space,
-           is_vertical_bar ? UI_UNIT_Y : space,
-           nullptr,
-           0.0,
-           0.0,
-           is_vertical_bar ? 1.0f : 0.0f,
-           0,
-           "");
+  uiBut *but = uiDefBut(block,
+                        but_type,
+                        0,
+                        "",
+                        0,
+                        0,
+                        space,
+                        is_vertical_bar ? UI_UNIT_Y : space,
+                        nullptr,
+                        0.0,
+                        0.0,
+                        0.0,
+                        0,
+                        "");
+
+  if (but_type == UI_BTYPE_SEPR_LINE) {
+    uiButSeparatorLine *but_line = static_cast<uiButSeparatorLine *>(but);
+    but_line->is_vertical = is_vertical_bar;
+  }
 }
 
 void uiItemS(uiLayout *layout)
diff --git a/source/blender/editors/interface/interface_widgets.cc b/source/blender/editors/interface/interface_widgets.cc
index 86c7912106b..6cbe5fa4713 100644
--- a/source/blender/editors/interface/interface_widgets.cc
+++ b/source/blender/editors/interface/interface_widgets.cc
@@ -3389,7 +3389,8 @@ static void ui_draw_but_HSV_v(uiBut *but, const rcti *rect)
 /** Separator line. */
 static void ui_draw_separator(const uiWidgetColors *wcol, uiBut *but, const rcti *rect)
 {
-  const bool vertical = but->a1 == 1.0f;
+  const uiButSeparatorLine *but_line = static_cast<uiButSeparatorLine *>(but);
+  const bool vertical = but_line->is_vertical;
   const int mid = vertical ? BLI_rcti_cent_x(rect) : BLI_rcti_cent_y(rect);
   const uchar col[4] = {
       wcol->text[0],