diff --git a/src/PhoneNumberUtil.php b/src/PhoneNumberUtil.php
index d8880db0..007794e4 100644
--- a/src/PhoneNumberUtil.php
+++ b/src/PhoneNumberUtil.php
@@ -2577,6 +2577,9 @@ public function formatOutOfCountryKeepingAlphaChars(PhoneNumber $number, string
         $regionCode = $this->getRegionCodeForCountryCode($countryCode);
         // Metadata cannot be null because the country calling code is valid.
         $metadataForRegion = $this->getMetadataForRegionOrCallingCode($countryCode, $regionCode);
+        // Strip any extension
+        $this->maybeStripExtension($formattedNumber);
+        // Append the formatted extension
         $this->maybeAppendFormattedExtension(
             $number,
             $metadataForRegion,
diff --git a/tests/core/PhoneNumberUtilTest.php b/tests/core/PhoneNumberUtilTest.php
index d31e5655..1dab19fc 100644
--- a/tests/core/PhoneNumberUtilTest.php
+++ b/tests/core/PhoneNumberUtilTest.php
@@ -875,6 +875,13 @@ public function testFormatOutOfCountryKeepingAlphaChars(): void
             $this->phoneUtil->formatOutOfCountryKeepingAlphaChars($alphaNumericNumber, RegionCode::BS)
         );
 
+        // Testing a number with extension.
+        $alphaNumericNumberWithExtn = $this->phoneUtil->parseAndKeepRawInput('800 SIX-flag ext. 1234', RegionCode::US);
+        $this->assertEquals(
+            '0011 1 800 SIX-FLAG extn. 1234',
+            $this->phoneUtil->formatOutOfCountryKeepingAlphaChars($alphaNumericNumberWithExtn, RegionCode::AU)
+        );
+
         // Testing that if the raw input doesn't exist, it is formatted using
         // formatOutOfCountryCallingNumber.
         $alphaNumericNumber->clearRawInput();