diff --git a/dom/html/nsGenericHTMLElement.cpp b/dom/html/nsGenericHTMLElement.cpp
index 8ae8240e3798..f3ca091fb0c5 100644
--- a/dom/html/nsGenericHTMLElement.cpp
+++ b/dom/html/nsGenericHTMLElement.cpp
@@ -1301,6 +1301,43 @@ nsGenericHTMLElement::ParseScrollingValue(const nsAString& aString,
   return aResult.ParseEnumValue(aString, kScrollingTable, false);
 }
 
+static inline void
+MapLangAttributeInto(const nsMappedAttributes* aAttributes, nsRuleData* aData)
+{
+  if (!(aData->mSIDs & (NS_STYLE_INHERIT_BIT(Font) |
+                        NS_STYLE_INHERIT_BIT(Text)))) {
+    return;
+  }
+
+  const nsAttrValue* langValue = aAttributes->GetAttr(nsGkAtoms::lang);
+  if (!langValue || langValue->Type() != nsAttrValue::eString) {
+    return;
+  }
+
+  if (aData->mSIDs & NS_STYLE_INHERIT_BIT(Font)) {
+    nsCSSValue* lang = aData->ValueForLang();
+    if (lang->GetUnit() == eCSSUnit_Null) {
+      lang->SetStringValue(langValue->GetStringValue(), eCSSUnit_Ident);
+    }
+  }
+  if (aData->mSIDs & NS_STYLE_INHERIT_BIT(Text)) {
+    nsCSSValue* emphasisPos = aData->ValueForTextEmphasisPosition();
+    if (emphasisPos->GetUnit() == eCSSUnit_Null) {
+      const nsAString& lang = langValue->GetStringValue();
+      if (nsStyleUtil::MatchesLanguagePrefix(lang, MOZ_UTF16("zh"))) {
+        emphasisPos->SetIntValue(NS_STYLE_TEXT_EMPHASIS_POSITION_DEFAULT_ZH,
+                                eCSSUnit_Enumerated);
+      } else if (nsStyleUtil::MatchesLanguagePrefix(lang, MOZ_UTF16("ja")) ||
+                 nsStyleUtil::MatchesLanguagePrefix(lang, MOZ_UTF16("mn"))) {
+        // This branch is currently no part of the spec.
+        // See bug 1040668 comment 69 and comment 75.
+        emphasisPos->SetIntValue(NS_STYLE_TEXT_EMPHASIS_POSITION_DEFAULT,
+                                eCSSUnit_Enumerated);
+      }
+    }
+  }
+}
+
 /**
  * Handle attributes common to all html elements
  */
@@ -1327,31 +1364,7 @@ nsGenericHTMLElement::MapCommonAttributesIntoExceptHidden(const nsMappedAttribut
     }
   }
 
-  const nsAttrValue* langValue = aAttributes->GetAttr(nsGkAtoms::lang);
-  if (langValue && langValue->Type() == nsAttrValue::eString) {
-    if (aData->mSIDs & NS_STYLE_INHERIT_BIT(Font)) {
-      nsCSSValue* lang = aData->ValueForLang();
-      if (lang->GetUnit() == eCSSUnit_Null) {
-        lang->SetStringValue(langValue->GetStringValue(), eCSSUnit_Ident);
-      }
-    }
-    if (aData->mSIDs & NS_STYLE_INHERIT_BIT(Text)) {
-      nsCSSValue* emphasisPos = aData->ValueForTextEmphasisPosition();
-      if (emphasisPos->GetUnit() == eCSSUnit_Null) {
-        const nsAString& lang = langValue->GetStringValue();
-        if (nsStyleUtil::MatchesLanguagePrefix(lang, MOZ_UTF16("zh"))) {
-          emphasisPos->SetIntValue(NS_STYLE_TEXT_EMPHASIS_POSITION_DEFAULT_ZH,
-                                   eCSSUnit_Enumerated);
-        } else if (nsStyleUtil::MatchesLanguagePrefix(lang, MOZ_UTF16("ja")) ||
-                   nsStyleUtil::MatchesLanguagePrefix(lang, MOZ_UTF16("mn"))) {
-          // This branch is currently no part of the spec.
-          // See bug 1040668 comment 69 and comment 75.
-          emphasisPos->SetIntValue(NS_STYLE_TEXT_EMPHASIS_POSITION_DEFAULT,
-                                   eCSSUnit_Enumerated);
-        }
-      }
-    }
-  }
+  MapLangAttributeInto(aAttributes, aData);
 }
 
 void