diff --git a/package.json b/package.json
index bdfbb8a..0433ff0 100644
--- a/package.json
+++ b/package.json
@@ -1,6 +1,6 @@
 {
   "name": "@tp/tp-popup",
-  "version": "1.3.0",
+  "version": "1.4.0",
   "description": "",
   "main": "tp-popup.js",
   "scripts": {
@@ -13,7 +13,7 @@
   "author": "trading_peter",
   "license": "Apache-2.0",
   "dependencies": {
-    "@tp/helpers": "^2.0.0",
+    "@tp/helpers": "^2.13.0",
     "@tp/tp-icon": "^1.0.1",
     "lit": "^3.0.0"
   }
diff --git a/tp-popup.js b/tp-popup.js
index 0a1d0dc..def3fa0 100644
--- a/tp-popup.js
+++ b/tp-popup.js
@@ -89,7 +89,12 @@ class TpPopup extends EventHelpers(Position(DomQuery(LitElement))) {
       alwaysToggle: { type: Boolean, reflect: true },
       halign: { type: String },
       valign: { type: String },
-      scrollTarget: { type: Object }
+      scrollTarget: { type: Object },
+      // When true, clamp the popup against its containing-block rect instead
+      // of the viewport. Enable for popups under an ancestor with transform /
+      // filter / contain:layout|paint, where position: fixed resolves against
+      // that ancestor and the viewport is the wrong clamp edge.
+      clampToContainer: { type: Boolean, reflect: true }
     };
   }
 
@@ -100,6 +105,7 @@ class TpPopup extends EventHelpers(Position(DomQuery(LitElement))) {
     this.halign = 'middle';
     this.valign = 'bottom';
     this.scrollTarget = document;
+    this.clampToContainer = false;
     this.fit = this.fit.bind(this);
     this._onDocClickHandler = () => this.close();
   }
@@ -165,7 +171,8 @@ class TpPopup extends EventHelpers(Position(DomQuery(LitElement))) {
     this._posFixed(this.shadowRoot.querySelector('.toggle'), this.$.content, {
       valign: this.valign || 'bottom',
       halign: this.halign || 'middle',
-      spacing: 5
+      spacing: 5,
+      clampToContainer: this.clampToContainer
     });
   }