diff --git a/Libraries/LibWeb/CSS/StyleComputer.cpp b/Libraries/LibWeb/CSS/StyleComputer.cpp
index c6d8125753..117f630286 100644
--- a/Libraries/LibWeb/CSS/StyleComputer.cpp
+++ b/Libraries/LibWeb/CSS/StyleComputer.cpp
@@ -711,6 +711,14 @@ void StyleComputer::collect_animation_into(DOM::AbstractElement abstract_element
if (style_value->is_unresolved())
style_value = Parser::Parser::resolve_unresolved_style_value(Parser::ParsingParams { abstract_element.document() }, abstract_element, PropertyNameAndID::from_id(property_id), style_value->as_unresolved());
+ // https://drafts.csswg.org/css-values-5/#invalid-at-computed-value-time
+ // When substitution results in a guaranteed-invalid value, treat it as unset
+ // (i.e. inherit for inherited properties, initial for non-inherited properties).
+ if (style_value->is_guaranteed_invalid()) {
+ specified_values.set(property_id, nullptr);
+ continue;
+ }
+
for_each_property_expanding_shorthands(property_id, *style_value, [&](PropertyID longhand_id, StyleValue const& longhand_value) {
auto physical_longhand_id = map_logical_alias_to_physical_property(longhand_id, LogicalAliasMappingContext { computed_properties.writing_mode(), computed_properties.direction() });
auto physical_longhand_id_bitmap_index = to_underlying(physical_longhand_id) - to_underlying(first_longhand_property_id);
diff --git a/Tests/LibWeb/Text/expected/css/animation-opacity-invalid-var.txt b/Tests/LibWeb/Text/expected/css/animation-opacity-invalid-var.txt
new file mode 100644
index 0000000000..d00491fd7e
--- /dev/null
+++ b/Tests/LibWeb/Text/expected/css/animation-opacity-invalid-var.txt
@@ -0,0 +1 @@
+1
diff --git a/Tests/LibWeb/Text/input/css/animation-opacity-invalid-var.html b/Tests/LibWeb/Text/input/css/animation-opacity-invalid-var.html
new file mode 100644
index 0000000000..de262cf46b
--- /dev/null
+++ b/Tests/LibWeb/Text/input/css/animation-opacity-invalid-var.html
@@ -0,0 +1,13 @@
+
+
+
+
+
+