diff --git a/components/layout_2020/flow/mod.rs b/components/layout_2020/flow/mod.rs
index 2187a15c7f5..b174c68ff3a 100644
--- a/components/layout_2020/flow/mod.rs
+++ b/components/layout_2020/flow/mod.rs
@@ -1969,11 +1969,12 @@ impl IndependentFormattingContext {
                 let max_box_size = style.content_max_box_size(containing_block, &pbm);
                 let min_box_size = style.content_min_box_size(containing_block, &pbm);
 
-                let available_inline_size = containing_block.inline_size - pbm_sums.inline_sum();
+                let available_inline_size =
+                    (containing_block.inline_size - pbm_sums.inline_sum()).max(Au::zero());
                 let available_block_size = containing_block
                     .block_size
                     .non_auto()
-                    .map(|block_size| block_size - pbm_sums.block_sum());
+                    .map(|block_size| (block_size - pbm_sums.block_sum()).max(Au::zero()));
                 let tentative_block_size = box_size
                     .block
                     .maybe_resolve_extrinsic(available_block_size)
diff --git a/tests/wpt/meta/MANIFEST.json b/tests/wpt/meta/MANIFEST.json
index 239e5bf47d6..beae54aaadf 100644
--- a/tests/wpt/meta/MANIFEST.json
+++ b/tests/wpt/meta/MANIFEST.json
@@ -569290,14 +569290,14 @@
       ]
      ],
      "keyword-sizes-on-floated-element.html": [
-      "adfffba8061aa983800822746a0cd5fc8f6f0fa8",
+      "42ea7ba26d7e1ffd26f8f12bad37e3b18abba0f6",
       [
        null,
        {}
       ]
      ],
      "keyword-sizes-on-inline-block.html": [
-      "d91d8e6ed9cd2ab7c7f0e418b7715fc88a03b4e1",
+      "7c41d902aa89c9f46a936dbac1d20b80bb5cdd98",
       [
        null,
        {}
diff --git a/tests/wpt/tests/css/css-sizing/keyword-sizes-on-floated-element.html b/tests/wpt/tests/css/css-sizing/keyword-sizes-on-floated-element.html
index adfffba8061..42ea7ba26d7 100644
--- a/tests/wpt/tests/css/css-sizing/keyword-sizes-on-floated-element.html
+++ b/tests/wpt/tests/css/css-sizing/keyword-sizes-on-floated-element.html
@@ -119,6 +119,12 @@
   <div class="test max-height stretch" data-expected-height="90">XXXXX XXXXX</div>
 </div>
 
+<!-- Stretch sizes can't result in a negative content size -->
+<div class="wrapper" style="width: 0px; height: 0px">
+  <div class="test width min-width max-width stretch" data-expected-width="10"></div>
+  <div class="test height min-height max-height stretch" data-expected-height="10"></div>
+</div>
+
 <!-- Indefinite stretch -->
 <div style="width: 100px; max-height: 100px">
   <div class="test height stretch indefinite" data-expected-height="30">X X</div>
diff --git a/tests/wpt/tests/css/css-sizing/keyword-sizes-on-inline-block.html b/tests/wpt/tests/css/css-sizing/keyword-sizes-on-inline-block.html
index d91d8e6ed9c..7c41d902aa8 100644
--- a/tests/wpt/tests/css/css-sizing/keyword-sizes-on-inline-block.html
+++ b/tests/wpt/tests/css/css-sizing/keyword-sizes-on-inline-block.html
@@ -125,6 +125,12 @@
   <div class="test max-height stretch" data-expected-height="90">XXXXX XXXXX</div>
 </div>
 
+<!-- Stretch sizes can't result in a negative content size -->
+<div class="wrapper" style="width: 0px; height: 0px">
+  <div class="test width min-width max-width stretch" data-expected-width="10"></div>
+  <div class="test height min-height max-height stretch" data-expected-height="10"></div>
+</div>
+
 <!-- Indefinite stretch -->
 <div class="wrapper" style="width: 100px; max-height: 100px">
   <div class="test height stretch indefinite" data-expected-height="30">X X</div>