diff --git a/components/layout/block.rs b/components/layout/block.rs
index fa91b847b20..0b10ef39000 100644
--- a/components/layout/block.rs
+++ b/components/layout/block.rs
@@ -1020,8 +1020,12 @@ impl BlockFlow {
                 self.base.position.size.block = cur_b;
             }
 
-            // Store the current set of floats in the flow so that flows that come later in the
+            // Translate the current set of floats back into the parent coordinate system in the
+            // inline direction, and store them in the flow so that flows that come later in the
             // document can access them.
+            floats.translate(LogicalSize::new(writing_mode,
+                                              self.fragment.inline_start_offset(),
+                                              Au(0)));
             self.base.floats = floats.clone();
             self.adjust_fragments_for_collapsed_margins_if_root(layout_context);
         } else {
diff --git a/components/layout/floats.rs b/components/layout/floats.rs
index 63fdc6da796..bd91acb657d 100644
--- a/components/layout/floats.rs
+++ b/components/layout/floats.rs
@@ -470,17 +470,22 @@ impl SpeculatedFloatPlacement {
             let block_flow = flow.as_block();
             if block_flow.formatting_context_type() != FormattingContextType::None {
                 *self = block_flow.base.speculated_float_placement_in;
+            }
 
-                if self.left > Au(0) || self.right > Au(0) {
-                    let speculated_inline_content_edge_offsets =
-                        block_flow.fragment.guess_inline_content_edge_offsets();
-                    if self.left > Au(0) && speculated_inline_content_edge_offsets.start > Au(0) {
-                        self.left = self.left + speculated_inline_content_edge_offsets.start
-                    }
-                    if self.right > Au(0) && speculated_inline_content_edge_offsets.end > Au(0) {
-                        self.right = self.right + speculated_inline_content_edge_offsets.end
-                    }
+            if self.left > Au(0) || self.right > Au(0) {
+                let speculated_inline_content_edge_offsets =
+                    block_flow.fragment.guess_inline_content_edge_offsets();
+                if self.left > Au(0) && speculated_inline_content_edge_offsets.start > Au(0) {
+                    self.left = self.left + speculated_inline_content_edge_offsets.start
                 }
+                if self.right > Au(0) && speculated_inline_content_edge_offsets.end > Au(0) {
+                    self.right = self.right + speculated_inline_content_edge_offsets.end
+                }
+            }
+
+            if block_flow.formatting_context_type() == FormattingContextType::None {
+                self.left = max(self.left, block_flow.base.speculated_float_placement_in.left);
+                self.right = max(self.right, block_flow.base.speculated_float_placement_in.right);
             }
         }
 
diff --git a/tests/wpt/mozilla/meta/MANIFEST.json b/tests/wpt/mozilla/meta/MANIFEST.json
index 4285757014f..be3c9a95e51 100644
--- a/tests/wpt/mozilla/meta/MANIFEST.json
+++ b/tests/wpt/mozilla/meta/MANIFEST.json
@@ -1608,6 +1608,18 @@
             "url": "/_mozilla/css/floated_table_with_margin_a.html"
           }
         ],
+        "css/floats_inline_margins_a.html": [
+          {
+            "path": "css/floats_inline_margins_a.html",
+            "references": [
+              [
+                "/_mozilla/css/floats_inline_margins_ref.html",
+                "=="
+              ]
+            ],
+            "url": "/_mozilla/css/floats_inline_margins_a.html"
+          }
+        ],
         "css/floats_margin_collapse_a.html": [
           {
             "path": "css/floats_margin_collapse_a.html",
@@ -8336,6 +8348,18 @@
           "url": "/_mozilla/css/floated_table_with_margin_a.html"
         }
       ],
+      "css/floats_inline_margins_a.html": [
+        {
+          "path": "css/floats_inline_margins_a.html",
+          "references": [
+            [
+              "/_mozilla/css/floats_inline_margins_ref.html",
+              "=="
+            ]
+          ],
+          "url": "/_mozilla/css/floats_inline_margins_a.html"
+        }
+      ],
       "css/floats_margin_collapse_a.html": [
         {
           "path": "css/floats_margin_collapse_a.html",
diff --git a/tests/wpt/mozilla/tests/css/floats_inline_margins_a.html b/tests/wpt/mozilla/tests/css/floats_inline_margins_a.html
new file mode 100644
index 00000000000..19b4910e6e0
--- /dev/null
+++ b/tests/wpt/mozilla/tests/css/floats_inline_margins_a.html
@@ -0,0 +1,27 @@
+<!DOCTYPE html>
+<meta charset="utf-8">
+<title></title>
+<link rel="match" href="floats_inline_margins_ref.html">
+<style>
+html, body, p {
+    margin: 0;
+    padding: 0;
+}
+div {
+    background-color: gold;
+    float: left;
+    height: 27px;
+    width: 27px;
+}
+#first {
+    margin-left: 27px;
+}
+</style>
+</head>
+<body>
+    <div></div>
+    <p id=first>submitted</p>
+    <p>x</p>
+</body>
+</html>
+
diff --git a/tests/wpt/mozilla/tests/css/floats_inline_margins_ref.html b/tests/wpt/mozilla/tests/css/floats_inline_margins_ref.html
new file mode 100644
index 00000000000..38da254f7d6
--- /dev/null
+++ b/tests/wpt/mozilla/tests/css/floats_inline_margins_ref.html
@@ -0,0 +1,24 @@
+<!DOCTYPE html>
+<meta charset="utf-8">
+<title></title>
+<style>
+html, body, p {
+    margin: 0;
+    padding: 0;
+}
+div {
+    background-color: gold;
+    float: left;
+    height: 27px;
+    width: 27px;
+    border-bottom: solid white 27px;
+}
+</style>
+</head>
+<body>
+    <div></div>
+    <p id=first>submitted</p>
+    <p>x</p>
+</body>
+</html>
+