diff --git a/apps/web/src/components/chat/AssistantCitationChip.browser.test.tsx b/apps/web/src/components/chat/AssistantCitationChip.browser.test.tsx
index 790fb481174e5..d5f3d6debba7b 100644
--- a/apps/web/src/components/chat/AssistantCitationChip.browser.test.tsx
+++ b/apps/web/src/components/chat/AssistantCitationChip.browser.test.tsx
@@ -152,3 +152,25 @@ describe("citation comment source disappearance", () => {
     expect(textarea()).toBeNull();
   });
 });
+
+describe("citation comment popup placement", () => {
+  it("opens inside the window when the cited line ends in a code block's horizontal overflow", async () => {
+    const pre = document.createElement("pre");
+    pre.style.cssText = "width: 120px; overflow-x: auto; white-space: pre; margin: 0";
+    pre.textContent = `${"x".repeat(400)}\ny`;
+    document.body.append(pre);
+    const range = document.createRange();
+    range.setStart(pre.firstChild!, 0);
+    range.setEnd(pre.firstChild!, 401);
+    sourceAnchor = { source: pre, range, viewport: document.body } as AssistantCitationSourceAnchor;
+    // The anchor is the selection's last rect: a narrow line-end rect past the window edge.
+    const rects = range.getClientRects();
+    expect(rects.item(rects.length - 1)!.left).toBeGreaterThan(window.innerWidth);
+
+    await mount();
+
+    const popup = document.querySelector('[data-slot="popover-popup"]')!.getBoundingClientRect();
+    expect(popup.left).toBeGreaterThanOrEqual(0);
+    expect(popup.right).toBeLessThanOrEqual(window.innerWidth);
+  });
+});
diff --git a/apps/web/src/components/chat/AssistantCitationChip.tsx b/apps/web/src/components/chat/AssistantCitationChip.tsx
index 741880d411614..6986aaaad593c 100644
--- a/apps/web/src/components/chat/AssistantCitationChip.tsx
+++ b/apps/web/src/components/chat/AssistantCitationChip.tsx
@@ -175,6 +175,10 @@ export function AssistantCitationChip({
               {...composerFloatingLayerProps}
               side={activeSourceAnchor ? "bottom" : "top"}
               align="end"
+              // The anchor is the quote's last line rect, which can lie past the window edge
+              // inside a code block's horizontal overflow. Without sticky, Base UI keeps the
+              // popup attached to that rect instead of shifting it into view.
+              sticky
               anchor={popupAnchor}
               initialFocus={() => {
                 commentInputRef.current?.focus({ preventScroll: true });
diff --git a/apps/web/src/components/ui/popover.tsx b/apps/web/src/components/ui/popover.tsx
index 08a10e143a3ff..4d3e7ea2d6263 100644
--- a/apps/web/src/components/ui/popover.tsx
+++ b/apps/web/src/components/ui/popover.tsx
@@ -40,6 +40,7 @@ function PopoverPopup({
   sideOffset = 4,
   alignOffset = 0,
   collisionAvoidance,
+  sticky,
   tooltipStyle = false,
   keepMounted = false,
   anchor,
@@ -53,6 +54,7 @@ function PopoverPopup({
   sideOffset?: PopoverPrimitive.Positioner.Props["sideOffset"];
   alignOffset?: PopoverPrimitive.Positioner.Props["alignOffset"];
   collisionAvoidance?: PopoverPrimitive.Positioner.Props["collisionAvoidance"];
+  sticky?: PopoverPrimitive.Positioner.Props["sticky"];
   tooltipStyle?: boolean;
   keepMounted?: PopoverPrimitive.Portal.Props["keepMounted"];
   anchor?: PopoverPrimitive.Positioner.Props["anchor"];
@@ -78,6 +80,7 @@ function PopoverPopup({
         alignOffset={alignOffset}
         anchor={anchor}
         collisionAvoidance={collisionAvoidance}
+        sticky={sticky}
         collisionPadding={variant === "panel" ? 0 : undefined}
         className={cn(
           "h-(--positioner-height) w-(--positioner-width) max-w-(--available-width) transition-transform data-instant:transition-none",