diff --git a/components/style/style_adjuster.rs b/components/style/style_adjuster.rs
index b855b937dfb..09bdb2a6522 100644
--- a/components/style/style_adjuster.rs
+++ b/components/style/style_adjuster.rs
@@ -150,6 +150,35 @@ impl<'a, 'b: 'a> StyleAdjuster<'a, 'b> {
         }
     }
 
+    /// -webkit-box with line-clamp and vertical orientation gets turned into
+    /// flow-root at computed-value time.
+    ///
+    /// This makes the element not be a flex container, with all that it
+    /// implies, but it should be safe. It matches blink, see
+    /// https://bugzilla.mozilla.org/show_bug.cgi?id=1786147#c10
+    fn adjust_for_webkit_line_clamp(&mut self) {
+        use crate::properties::longhands::_moz_box_orient::computed_value::T as BoxOrient;
+        use crate::values::specified::box_::{DisplayOutside, DisplayInside};
+        let box_style= self.style.get_box();
+        if box_style.clone__webkit_line_clamp().is_none() {
+            return;
+        }
+        let disp = box_style.clone_display();
+        if disp.inside() != DisplayInside::WebkitBox {
+            return;
+        }
+        if self.style.get_xul().clone__moz_box_orient() != BoxOrient::Vertical {
+            return;
+        }
+        let new_display = if disp.outside() == DisplayOutside::Block {
+            Display::FlowRoot
+        } else {
+            debug_assert_eq!(disp.outside(), DisplayOutside::Inline);
+            Display::InlineBlock
+        };
+        self.style.mutate_box().set_adjusted_display(new_display, false);
+    }
+
     /// CSS 2.1 section 9.7:
     ///
     ///    If 'position' has the value 'absolute' or 'fixed', [...] the computed
@@ -856,6 +885,7 @@ impl<'a, 'b: 'a> StyleAdjuster<'a, 'b> {
         }
         self.adjust_for_top_layer();
         self.blockify_if_necessary(layout_parent_style, element);
+        self.adjust_for_webkit_line_clamp();
         self.adjust_for_position();
         self.adjust_for_overflow();
         #[cfg(feature = "gecko")]