diff --git a/cpp/src/phonenumbers/phonenumberutil.cc b/cpp/src/phonenumbers/phonenumberutil.cc
index 705c934d92..cd7d231a61 100644
--- a/cpp/src/phonenumbers/phonenumberutil.cc
+++ b/cpp/src/phonenumbers/phonenumberutil.cc
@@ -1222,7 +1222,8 @@ void PhoneNumberUtil::FormatByPattern(
     FormatNsnUsingPattern(national_significant_number, num_format_copy,
                           number_format, formatted_number);
   }
-  MaybeAppendFormattedExtension(number, *metadata, NATIONAL, formatted_number);
+  MaybeAppendFormattedExtension(number, *metadata, number_format,
+                                formatted_number);
   PrefixNumberWithCountryCallingCode(country_calling_code, number_format,
                                      formatted_number);
 }
diff --git a/cpp/test/phonenumbers/phonenumberutil_test.cc b/cpp/test/phonenumbers/phonenumberutil_test.cc
index 97cf1f08a4..4ff7c217f1 100644
--- a/cpp/test/phonenumbers/phonenumberutil_test.cc
+++ b/cpp/test/phonenumbers/phonenumberutil_test.cc
@@ -1333,6 +1333,12 @@ TEST_F(PhoneNumberUtilTest, FormatByPattern) {
                               number_formats,
                               &formatted_number);
   EXPECT_EQ("tel:+1-650-253-0000", formatted_number);
+  PhoneNumber test_number_with_extension(test_number);
+  test_number_with_extension.set_extension("1234");
+  phone_util_.FormatByPattern(test_number_with_extension,
+                              PhoneNumberUtil::RFC3966, number_formats,
+                              &formatted_number);
+  EXPECT_EQ("tel:+1-650-253-0000;ext=1234", formatted_number);
 
   // $NP is set to '1' for the US. Here we check that for other NANPA countries
   // the US rules are followed.
diff --git a/pending_code_changes.txt b/pending_code_changes.txt
index 8b13789179..57000973bf 100644
--- a/pending_code_changes.txt
+++ b/pending_code_changes.txt
@@ -1 +1,2 @@
-
+Code changes:
+ - Fixed FormatByPattern in the C++ version to format the extension for the requested number format, so RFC3966 output uses ";ext=" as in the Java version.
\ No newline at end of file