diff --git a/components/style/properties/declaration_block.rs b/components/style/properties/declaration_block.rs
index 2cb5cba4874..f10da7a7cb4 100644
--- a/components/style/properties/declaration_block.rs
+++ b/components/style/properties/declaration_block.rs
@@ -288,10 +288,15 @@ impl PropertyDeclarationBlock {
         }
         let important_count = &mut self.important_count;
         let mut removed_at_least_one = false;
+        let longhands = &mut self.longhands;
         self.declarations.retain(|&(ref declaration, importance)| {
-            let remove = declaration.id().is_or_is_longhand_of(property);
+            let id = declaration.id();
+            let remove = id.is_or_is_longhand_of(property);
             if remove {
                 removed_at_least_one = true;
+                if let PropertyDeclarationId::Longhand(id) = id {
+                    longhands.remove(id)
+                }
                 if importance.important() {
                     *important_count -= 1
                 }
@@ -299,9 +304,8 @@ impl PropertyDeclarationBlock {
             !remove
         });
 
-        if let PropertyId::Longhand(id) = *property {
+        if let PropertyId::Longhand(_) = *property {
             debug_assert!(removed_at_least_one);
-            self.longhands.remove(id);
         }
         removed_at_least_one
     }
diff --git a/tests/wpt/mozilla/meta/MANIFEST.json b/tests/wpt/mozilla/meta/MANIFEST.json
index a20dffa1557..d554b574926 100644
--- a/tests/wpt/mozilla/meta/MANIFEST.json
+++ b/tests/wpt/mozilla/meta/MANIFEST.json
@@ -20620,7 +20620,7 @@
    "support"
   ],
   "css/bug_1345483.html": [
-   "d5e1649c88102f27da5fe1ac16715cfee7f70f84",
+   "41b55af9d5c95910b1af74c0fbffb24e20bbe869",
    "testharness"
   ],
   "css/button_css_width.html": [
diff --git a/tests/wpt/mozilla/meta/css/bug_1345483.html.ini b/tests/wpt/mozilla/meta/css/bug_1345483.html.ini
deleted file mode 100644
index 9d7d959bdc7..00000000000
--- a/tests/wpt/mozilla/meta/css/bug_1345483.html.ini
+++ /dev/null
@@ -1,3 +0,0 @@
-[bug_1345483.html]
-  type: testharness
-  expected: CRASH
diff --git a/tests/wpt/mozilla/tests/css/bug_1345483.html b/tests/wpt/mozilla/tests/css/bug_1345483.html
index 595a799c9b7..87d0d357c63 100644
--- a/tests/wpt/mozilla/tests/css/bug_1345483.html
+++ b/tests/wpt/mozilla/tests/css/bug_1345483.html
@@ -8,8 +8,8 @@ test(function() {
     var style = document.documentElement.style;
     style.marginTop = "0";
     assert_equals(style.marginTop, "0px");
-    style.margin = null;  // This fails to unset a bit in a LonghandIdSet
+    style.margin = null;  // This used to fail to unset a bit in a LonghandIdSet
     assert_equals(style.marginTop, "");
-    style.marginTop = null;  // This finds the bit and expect to find a corresponding declarations.
+    style.marginTop = null;  // This would find the bit and expect to find a corresponding declarations.
 }, "regression for bug 1345483")
 </script>