diff --git a/mozilla/content/html/style/src/nsCSSDeclaration.cpp b/mozilla/content/html/style/src/nsCSSDeclaration.cpp
index 84df769f526..46a5b2eec2b 100644
--- a/mozilla/content/html/style/src/nsCSSDeclaration.cpp
+++ b/mozilla/content/html/style/src/nsCSSDeclaration.cpp
@@ -990,6 +990,10 @@ nsCSSDeclaration::TryOverflowShorthand(nsAString & aString,
     GetValueOrImportantValue(eCSSProperty_overflow_x, xValue);
     GetValueOrImportantValue(eCSSProperty_overflow_y, yValue);
     if (xValue == yValue) {
+      AppendASCIItoUTF16(nsCSSProps::GetStringValue(eCSSProperty_overflow),
+                         aString);
+      aString.AppendLiteral(": ");
+
       AppendCSSValueToString(eCSSProperty_overflow_x, xValue, aString);
       AppendImportanceToString(isImportant, aString);
       aString.AppendLiteral("; ");
diff --git a/mozilla/layout/style/nsCSSDeclaration.cpp b/mozilla/layout/style/nsCSSDeclaration.cpp
index 84df769f526..46a5b2eec2b 100644
--- a/mozilla/layout/style/nsCSSDeclaration.cpp
+++ b/mozilla/layout/style/nsCSSDeclaration.cpp
@@ -990,6 +990,10 @@ nsCSSDeclaration::TryOverflowShorthand(nsAString & aString,
     GetValueOrImportantValue(eCSSProperty_overflow_x, xValue);
     GetValueOrImportantValue(eCSSProperty_overflow_y, yValue);
     if (xValue == yValue) {
+      AppendASCIItoUTF16(nsCSSProps::GetStringValue(eCSSProperty_overflow),
+                         aString);
+      aString.AppendLiteral(": ");
+
       AppendCSSValueToString(eCSSProperty_overflow_x, xValue, aString);
       AppendImportanceToString(isImportant, aString);
       aString.AppendLiteral("; ");