diff --git a/components/layout_2020/flow/mod.rs b/components/layout_2020/flow/mod.rs
index 98a62302264..577070fbdab 100644
--- a/components/layout_2020/flow/mod.rs
+++ b/components/layout_2020/flow/mod.rs
@@ -250,7 +250,8 @@ fn calculate_inline_content_size_for_block_level_boxes(
             BlockLevelBox::OutOfFlowFloatBox(ref mut float_box) => {
                 let size = float_box
                     .contents
-                    .outer_inline_content_sizes(layout_context, writing_mode);
+                    .outer_inline_content_sizes(layout_context, writing_mode)
+                    .max(ContentSizes::zero());
                 let style_box = &float_box.contents.style().get_box();
                 Some((size, style_box.float, style_box.clear))
             },
@@ -259,14 +260,17 @@ fn calculate_inline_content_size_for_block_level_boxes(
             } => {
                 let size = sizing::outer_inline(&style, writing_mode, || {
                     contents.inline_content_sizes(layout_context, style.writing_mode)
-                });
+                })
+                .max(ContentSizes::zero());
                 // A block in the same BFC can overlap floats, it's not moved next to them,
                 // so we shouldn't add its size to the size of the floats.
                 // Instead, we treat it like an independent block with 'clear: both'.
                 Some((size, Float::None, Clear::Both))
             },
             BlockLevelBox::Independent(ref mut independent) => {
-                let size = independent.outer_inline_content_sizes(layout_context, writing_mode);
+                let size = independent
+                    .outer_inline_content_sizes(layout_context, writing_mode)
+                    .max(ContentSizes::zero());
                 Some((size, Float::None, independent.style().get_box().clear))
             },
         }