diff --git a/dom/mathml/MathMLElement.cpp b/dom/mathml/MathMLElement.cpp
index 0ceade64a3e7..d58930bc834d 100644
--- a/dom/mathml/MathMLElement.cpp
+++ b/dom/mathml/MathMLElement.cpp
@@ -528,9 +528,8 @@ void MathMLElement::MapMathMLAttributesInto(
     if (!ParseNumericValue(str, fontSize, flags, nullptr) &&
         parseSizeKeywords) {
       static const char sizes[3][7] = {"small", "normal", "big"};
-      static const int32_t values[MOZ_ARRAY_LENGTH(sizes)] = {
-          NS_STYLE_FONT_SIZE_SMALL, NS_STYLE_FONT_SIZE_MEDIUM,
-          NS_STYLE_FONT_SIZE_LARGE};
+      static const StyleFontSize values[MOZ_ARRAY_LENGTH(sizes)] = {
+          StyleFontSize::Small, StyleFontSize::Medium, StyleFontSize::Large};
       str.CompressWhitespace();
       for (uint32_t i = 0; i < ArrayLength(sizes); ++i) {
         if (str.EqualsASCII(sizes[i])) {
diff --git a/layout/style/ServoBindings.toml b/layout/style/ServoBindings.toml
index b8e1788a9f56..d7cf1b4df061 100644
--- a/layout/style/ServoBindings.toml
+++ b/layout/style/ServoBindings.toml
@@ -166,6 +166,7 @@ rusty-enums = [
     "mozilla::StyleBlend",
     "mozilla::StyleMaskComposite",
     "mozilla::StyleControlCharacterVisibility",
+    "mozilla::StyleFontSize",
 ]
 whitelist-vars = [
     "NS_ATTRVALUE_.*",
diff --git a/layout/style/nsStyleConsts.h b/layout/style/nsStyleConsts.h
index fc7bc25f69f3..693e37bc0e41 100644
--- a/layout/style/nsStyleConsts.h
+++ b/layout/style/nsStyleConsts.h
@@ -375,19 +375,19 @@ enum class StyleFlexWrap : uint8_t {
 #define NS_STYLE_ORDER_INITIAL 0
 
 // See nsStyleFont
-#define NS_STYLE_FONT_SIZE_XXSMALL 0
-#define NS_STYLE_FONT_SIZE_XSMALL 1
-#define NS_STYLE_FONT_SIZE_SMALL 2
-#define NS_STYLE_FONT_SIZE_MEDIUM 3
-#define NS_STYLE_FONT_SIZE_LARGE 4
-#define NS_STYLE_FONT_SIZE_XLARGE 5
-#define NS_STYLE_FONT_SIZE_XXLARGE 6
-#define NS_STYLE_FONT_SIZE_XXXLARGE \
-  7  // Only used by <font size="7">. Not specifiable in CSS.
-#define NS_STYLE_FONT_SIZE_LARGER 8
-#define NS_STYLE_FONT_SIZE_SMALLER 9
-#define NS_STYLE_FONT_SIZE_NO_KEYWORD \
-  10  // Used by Servo to track the "no keyword" case
+enum class StyleFontSize : uint8_t {
+  Xxsmall = 0,
+  Xsmall,
+  Small,
+  Medium,
+  Large,
+  Xlarge,
+  Xxlarge,
+  Xxxlarge,
+  Larger,
+  Smaller,
+  NoKeyword  // Used by Servo to track the "no keyword" case
+};
 
 #define NS_STYLE_MASONRY_PLACEMENT_PACK (1 << 0)
 #define NS_STYLE_MASONRY_ORDER_DEFINITE_FIRST (1 << 1)
diff --git a/layout/style/nsStyleStruct.cpp b/layout/style/nsStyleStruct.cpp
index ac1c7c5f9d84..f5f03b4888f5 100644
--- a/layout/style/nsStyleStruct.cpp
+++ b/layout/style/nsStyleStruct.cpp
@@ -245,7 +245,7 @@ nsStyleFont::nsStyleFont(const Document& aDocument)
       mSize(ZoomText(aDocument, mFont.size)),
       mFontSizeFactor(1.0),
       mFontSizeOffset(0),
-      mFontSizeKeyword(NS_STYLE_FONT_SIZE_MEDIUM),
+      mFontSizeKeyword(StyleFontSize::Medium),
       mGenericID(StyleGenericFontFamily::None),
       mScriptLevel(0),
       mMathVariant(NS_MATHML_MATHVARIANT_NONE),
diff --git a/layout/style/nsStyleStruct.h b/layout/style/nsStyleStruct.h
index c50087f745c9..066d1b47510f 100644
--- a/layout/style/nsStyleStruct.h
+++ b/layout/style/nsStyleStruct.h
@@ -102,9 +102,8 @@ struct MOZ_NEEDS_MEMMOVABLE_MEMBERS nsStyleFont {
   // and if so if it has been modified by a factor/offset
   float mFontSizeFactor;
   nscoord mFontSizeOffset;
-  uint8_t mFontSizeKeyword;  // NS_STYLE_FONT_SIZE_*, is
-                             // NS_STYLE_FONT_SIZE_NO_KEYWORD when not
-                             // keyword-derived
+  mozilla::StyleFontSize mFontSizeKeyword;  // StyleFontSize is Nokeyword when
+                                            // not keyword-derived
 
   mozilla::StyleGenericFontFamily mGenericID;
 
diff --git a/servo/components/style/properties/gecko.mako.rs b/servo/components/style/properties/gecko.mako.rs
index 545e8cc77b54..8b10d71c1466 100644
--- a/servo/components/style/properties/gecko.mako.rs
+++ b/servo/components/style/properties/gecko.mako.rs
@@ -953,19 +953,19 @@ fn static_assert() {
 
         if let Some(info) = v.keyword_info {
             self.gecko.mFontSizeKeyword = match info.kw {
-                KeywordSize::XXSmall => structs::NS_STYLE_FONT_SIZE_XXSMALL,
-                KeywordSize::XSmall => structs::NS_STYLE_FONT_SIZE_XSMALL,
-                KeywordSize::Small => structs::NS_STYLE_FONT_SIZE_SMALL,
-                KeywordSize::Medium => structs::NS_STYLE_FONT_SIZE_MEDIUM,
-                KeywordSize::Large => structs::NS_STYLE_FONT_SIZE_LARGE,
-                KeywordSize::XLarge => structs::NS_STYLE_FONT_SIZE_XLARGE,
-                KeywordSize::XXLarge => structs::NS_STYLE_FONT_SIZE_XXLARGE,
-                KeywordSize::XXXLarge => structs::NS_STYLE_FONT_SIZE_XXXLARGE,
-            } as u8;
+                KeywordSize::XXSmall => structs::StyleFontSize::Xxsmall,
+                KeywordSize::XSmall => structs::StyleFontSize::Xsmall,
+                KeywordSize::Small => structs::StyleFontSize::Small,
+                KeywordSize::Medium => structs::StyleFontSize::Medium,
+                KeywordSize::Large => structs::StyleFontSize::Large,
+                KeywordSize::XLarge => structs::StyleFontSize::Xxlarge,
+                KeywordSize::XXLarge => structs::StyleFontSize::Xxlarge,
+                KeywordSize::XXXLarge => structs::StyleFontSize::Xxxlarge,
+            };
             self.gecko.mFontSizeFactor = info.factor;
             self.gecko.mFontSizeOffset = info.offset.to_i32_au();
         } else {
-            self.gecko.mFontSizeKeyword = structs::NS_STYLE_FONT_SIZE_NO_KEYWORD as u8;
+            self.gecko.mFontSizeKeyword = structs::StyleFontSize::NoKeyword;
             self.gecko.mFontSizeFactor = 1.;
             self.gecko.mFontSizeOffset = 0;
         }
@@ -974,16 +974,16 @@ fn static_assert() {
     pub fn clone_font_size(&self) -> FontSize {
         use crate::values::specified::font::{KeywordInfo, KeywordSize};
         let size = Au(self.gecko.mSize).into();
-        let kw = match self.gecko.mFontSizeKeyword as u32 {
-            structs::NS_STYLE_FONT_SIZE_XXSMALL => KeywordSize::XXSmall,
-            structs::NS_STYLE_FONT_SIZE_XSMALL => KeywordSize::XSmall,
-            structs::NS_STYLE_FONT_SIZE_SMALL => KeywordSize::Small,
-            structs::NS_STYLE_FONT_SIZE_MEDIUM => KeywordSize::Medium,
-            structs::NS_STYLE_FONT_SIZE_LARGE => KeywordSize::Large,
-            structs::NS_STYLE_FONT_SIZE_XLARGE => KeywordSize::XLarge,
-            structs::NS_STYLE_FONT_SIZE_XXLARGE => KeywordSize::XXLarge,
-            structs::NS_STYLE_FONT_SIZE_XXXLARGE => KeywordSize::XXXLarge,
-            structs::NS_STYLE_FONT_SIZE_NO_KEYWORD => {
+        let kw = match self.gecko.mFontSizeKeyword {
+            structs::StyleFontSize::Xxsmall => KeywordSize::XXSmall,
+            structs::StyleFontSize::Xsmall => KeywordSize::XSmall,
+            structs::StyleFontSize::Small => KeywordSize::Small,
+            structs::StyleFontSize::Medium => KeywordSize::Medium,
+            structs::StyleFontSize::Large => KeywordSize::Large,
+            structs::StyleFontSize::Xlarge => KeywordSize::XLarge,
+            structs::StyleFontSize::Xxlarge => KeywordSize::XXLarge,
+            structs::StyleFontSize::Xxxlarge => KeywordSize::XXXLarge,
+            structs::StyleFontSize::NoKeyword => {
                 return FontSize {
                     size,
                     keyword_info: None,