diff --git a/Libraries/LibWeb/CSS/ComputedProperties.cpp b/Libraries/LibWeb/CSS/ComputedProperties.cpp
index 89330897b58..966722f3188 100644
--- a/Libraries/LibWeb/CSS/ComputedProperties.cpp
+++ b/Libraries/LibWeb/CSS/ComputedProperties.cpp
@@ -1008,8 +1008,11 @@ Vector<TextDecorationLine> ComputedProperties::text_decoration_line() const
         return lines;
     }
 
-    if (value.is_keyword() && value.to_keyword() == Keyword::None)
-        return {};
+    if (value.is_keyword()) {
+        if (value.to_keyword() == Keyword::None)
+            return {};
+        return { keyword_to_text_decoration_line(value.to_keyword()).release_value() };
+    }
 
     dbgln("FIXME: Unsupported value for text-decoration-line: {}", value.to_string(CSSStyleValue::SerializationMode::Normal));
     return {};
diff --git a/Libraries/LibWeb/CSS/Enums.json b/Libraries/LibWeb/CSS/Enums.json
index 6b03f3f473c..eb328f1d00c 100644
--- a/Libraries/LibWeb/CSS/Enums.json
+++ b/Libraries/LibWeb/CSS/Enums.json
@@ -545,7 +545,9 @@
     "underline",
     "overline",
     "line-through",
-    "blink"
+    "blink",
+    "spelling-error",
+    "grammar-error"
   ],
   "text-decoration-style": [
     "dashed",
diff --git a/Libraries/LibWeb/CSS/Keywords.json b/Libraries/LibWeb/CSS/Keywords.json
index 5c6267ed0b9..82a1d38bd59 100644
--- a/Libraries/LibWeb/CSS/Keywords.json
+++ b/Libraries/LibWeb/CSS/Keywords.json
@@ -190,6 +190,7 @@
   "fullscreen",
   "grab",
   "grabbing",
+  "grammar-error",
   "graytext",
   "grid",
   "groove",
@@ -404,6 +405,7 @@
   "space-around",
   "space-between",
   "space-evenly",
+  "spelling-error",
   "square",
   "square-button",
   "srgb",
diff --git a/Libraries/LibWeb/CSS/Parser/PropertyParsing.cpp b/Libraries/LibWeb/CSS/Parser/PropertyParsing.cpp
index 03b0b84e6a3..896253fe0b7 100644
--- a/Libraries/LibWeb/CSS/Parser/PropertyParsing.cpp
+++ b/Libraries/LibWeb/CSS/Parser/PropertyParsing.cpp
@@ -3510,6 +3510,8 @@ RefPtr<CSSStyleValue> Parser::parse_text_decoration_line_value(TokenStream<Compo
 {
     StyleValueVector style_values;
 
+    bool includes_spelling_or_grammar_error_value = false;
+
     while (tokens.has_next_token()) {
         auto maybe_value = parse_css_value_for_property(PropertyID::TextDecorationLine, tokens);
         if (!maybe_value)
@@ -3522,6 +3524,9 @@ RefPtr<CSSStyleValue> Parser::parse_text_decoration_line_value(TokenStream<Compo
                     break;
                 return value;
             }
+            if (first_is_one_of(*maybe_line, TextDecorationLine::SpellingError, TextDecorationLine::GrammarError)) {
+                includes_spelling_or_grammar_error_value = true;
+            }
             if (style_values.contains_slow(value))
                 break;
             style_values.append(move(value));
@@ -3534,6 +3539,13 @@ RefPtr<CSSStyleValue> Parser::parse_text_decoration_line_value(TokenStream<Compo
     if (style_values.is_empty())
         return nullptr;
 
+    // These can only appear on their own.
+    if (style_values.size() > 1 && includes_spelling_or_grammar_error_value)
+        return nullptr;
+
+    if (style_values.size() == 1)
+        return *style_values.first();
+
     quick_sort(style_values, [](auto& left, auto& right) {
         return *keyword_to_text_decoration_line(left->to_keyword()) < *keyword_to_text_decoration_line(right->to_keyword());
     });
diff --git a/Libraries/LibWeb/Painting/PaintableBox.cpp b/Libraries/LibWeb/Painting/PaintableBox.cpp
index 70f6c55050f..d7ae415cc31 100644
--- a/Libraries/LibWeb/Painting/PaintableBox.cpp
+++ b/Libraries/LibWeb/Painting/PaintableBox.cpp
@@ -682,6 +682,7 @@ void paint_text_decoration(PaintContext& context, TextPaintable const& paintable
     auto baseline = fragment.baseline();
 
     auto line_color = paintable.computed_values().text_decoration_color();
+    auto line_style = paintable.computed_values().text_decoration_style();
     auto const& text_paintable = static_cast<TextPaintable const&>(fragment.paintable());
     auto device_line_thickness = context.rounded_device_pixels(text_paintable.text_decoration_thickness());
 
@@ -690,6 +691,24 @@ void paint_text_decoration(PaintContext& context, TextPaintable const& paintable
         DevicePixelPoint line_start_point {};
         DevicePixelPoint line_end_point {};
 
+        if (line == CSS::TextDecorationLine::SpellingError) {
+            // https://drafts.csswg.org/css-text-decor-4/#valdef-text-decoration-line-spelling-error
+            // This value indicates the type of text decoration used by the user agent to highlight spelling mistakes.
+            // Its appearance is UA-defined, and may be platform-dependent. It is often rendered as a red wavy underline.
+            line_color = Color::Red;
+            device_line_thickness = context.rounded_device_pixels(1);
+            line_style = CSS::TextDecorationStyle::Wavy;
+            line = CSS::TextDecorationLine::Underline;
+        } else if (line == CSS::TextDecorationLine::GrammarError) {
+            // https://drafts.csswg.org/css-text-decor-4/#valdef-text-decoration-line-grammar-error
+            // This value indicates the type of text decoration used by the user agent to highlight grammar mistakes.
+            // Its appearance is UA defined, and may be platform-dependent. It is often rendered as a green wavy underline.
+            line_color = Color::DarkGreen;
+            device_line_thickness = context.rounded_device_pixels(1);
+            line_style = CSS::TextDecorationStyle::Wavy;
+            line = CSS::TextDecorationLine::Underline;
+        }
+
         switch (line) {
         case CSS::TextDecorationLine::None:
             return;
@@ -710,9 +729,13 @@ void paint_text_decoration(PaintContext& context, TextPaintable const& paintable
         case CSS::TextDecorationLine::Blink:
             // Conforming user agents may simply not blink the text
             return;
+        case CSS::TextDecorationLine::SpellingError:
+        case CSS::TextDecorationLine::GrammarError:
+            // Handled above.
+            VERIFY_NOT_REACHED();
         }
 
-        switch (paintable.computed_values().text_decoration_style()) {
+        switch (line_style) {
         case CSS::TextDecorationStyle::Solid:
             painter.draw_line(line_start_point.to_type<int>(), line_end_point.to_type<int>(), line_color, device_line_thickness.value(), Gfx::LineStyle::Solid);
             break;
@@ -742,7 +765,24 @@ void paint_text_decoration(PaintContext& context, TextPaintable const& paintable
             painter.draw_line(line_start_point.to_type<int>(), line_end_point.to_type<int>(), line_color, device_line_thickness.value(), Gfx::LineStyle::Dotted);
             break;
         case CSS::TextDecorationStyle::Wavy:
-            painter.draw_triangle_wave(line_start_point.to_type<int>(), line_end_point.to_type<int>(), line_color, device_line_thickness.value() + 1, device_line_thickness.value());
+            auto amplitude = device_line_thickness.value() * 3;
+            switch (line) {
+            case CSS::TextDecorationLine::Underline:
+                line_start_point.translate_by(0, device_line_thickness + context.rounded_device_pixels(1));
+                line_end_point.translate_by(0, device_line_thickness + context.rounded_device_pixels(1));
+                break;
+            case CSS::TextDecorationLine::Overline:
+                line_start_point.translate_by(0, -device_line_thickness - context.rounded_device_pixels(1));
+                line_end_point.translate_by(0, -device_line_thickness - context.rounded_device_pixels(1));
+                break;
+            case CSS::TextDecorationLine::LineThrough:
+                line_start_point.translate_by(0, -device_line_thickness / 2);
+                line_end_point.translate_by(0, -device_line_thickness / 2);
+                break;
+            default:
+                VERIFY_NOT_REACHED();
+            }
+            painter.draw_triangle_wave(line_start_point.to_type<int>(), line_end_point.to_type<int>(), line_color, amplitude, device_line_thickness.value());
             break;
         }
     }
diff --git a/Tests/LibWeb/Screenshot/images/text-decorations.png b/Tests/LibWeb/Screenshot/images/text-decorations.png
index 74bf0e3938f..dfb47c2b2b6 100644
Binary files a/Tests/LibWeb/Screenshot/images/text-decorations.png and b/Tests/LibWeb/Screenshot/images/text-decorations.png differ
diff --git a/Tests/LibWeb/Screenshot/input/text-decorations.html b/Tests/LibWeb/Screenshot/input/text-decorations.html
index 0ec0b414cfa..05cf67a12e8 100644
--- a/Tests/LibWeb/Screenshot/input/text-decorations.html
+++ b/Tests/LibWeb/Screenshot/input/text-decorations.html
@@ -8,6 +8,8 @@
     .strikethrough { text-decoration: line-through dotted green 5px; }
     .current-color { color: #8B4513; text-decoration: underline; }
     .overboard { text-decoration: double overline underline line-through magenta; }
+    .spelling-error { text-decoration: spelling-error; }
+    .grammar-error { text-decoration: grammar-error; }
 </style>
 </head>
 <body>
@@ -17,5 +19,7 @@
 	<p class="blink">FREE!</p>
 	<p class="current-color">This underline should match the text color</p>
 	<p class="overboard">This should have an underline, overline and line-through, all in glorious magenta.</p>
+	<p class="spelling-error">This should look like a spelling error.</p>
+	<p class="grammar-error">This should look like a grammar error.</p>
 </body>
 </html>
diff --git a/Tests/LibWeb/Text/expected/wpt-import/css/css-text-decor/parsing/text-decoration-line-computed.txt b/Tests/LibWeb/Text/expected/wpt-import/css/css-text-decor/parsing/text-decoration-line-computed.txt
index 4bf73195b20..7e200ec73e3 100644
--- a/Tests/LibWeb/Text/expected/wpt-import/css/css-text-decor/parsing/text-decoration-line-computed.txt
+++ b/Tests/LibWeb/Text/expected/wpt-import/css/css-text-decor/parsing/text-decoration-line-computed.txt
@@ -2,8 +2,7 @@ Harness status: OK
 
 Found 18 tests
 
-16 Pass
-2 Fail
+18 Pass
 Pass	Property text-decoration-line value 'none'
 Pass	Property text-decoration-line value 'underline'
 Pass	Property text-decoration-line value 'overline'
@@ -20,5 +19,5 @@ Pass	Property text-decoration-line value 'underline overline blink'
 Pass	Property text-decoration-line value 'underline line-through blink'
 Pass	Property text-decoration-line value 'overline line-through blink'
 Pass	Property text-decoration-line value 'underline overline line-through blink'
-Fail	Property text-decoration-line value 'spelling-error'
-Fail	Property text-decoration-line value 'grammar-error'
\ No newline at end of file
+Pass	Property text-decoration-line value 'spelling-error'
+Pass	Property text-decoration-line value 'grammar-error'
\ No newline at end of file
diff --git a/Tests/LibWeb/Text/expected/wpt-import/css/css-text-decor/parsing/text-decoration-line-valid.txt b/Tests/LibWeb/Text/expected/wpt-import/css/css-text-decor/parsing/text-decoration-line-valid.txt
index 1bbd4f0b608..1ddf11c6b53 100644
--- a/Tests/LibWeb/Text/expected/wpt-import/css/css-text-decor/parsing/text-decoration-line-valid.txt
+++ b/Tests/LibWeb/Text/expected/wpt-import/css/css-text-decor/parsing/text-decoration-line-valid.txt
@@ -2,8 +2,7 @@ Harness status: OK
 
 Found 67 tests
 
-65 Pass
-2 Fail
+67 Pass
 Pass	e.style['text-decoration-line'] = "none" should set the property value
 Pass	e.style['text-decoration-line'] = "underline" should set the property value
 Pass	e.style['text-decoration-line'] = "overline" should set the property value
@@ -69,5 +68,5 @@ Pass	e.style['text-decoration-line'] = "blink overline underline line-through" s
 Pass	e.style['text-decoration-line'] = "blink overline line-through underline" should set the property value
 Pass	e.style['text-decoration-line'] = "blink line-through underline overline" should set the property value
 Pass	e.style['text-decoration-line'] = "blink line-through overline underline" should set the property value
-Fail	e.style['text-decoration-line'] = "spelling-error" should set the property value
-Fail	e.style['text-decoration-line'] = "grammar-error" should set the property value
\ No newline at end of file
+Pass	e.style['text-decoration-line'] = "spelling-error" should set the property value
+Pass	e.style['text-decoration-line'] = "grammar-error" should set the property value
\ No newline at end of file