diff --git a/ext/sodium/libsodium.c b/ext/sodium/libsodium.c
index 57a34d5ec841..7c80de9cbf16 100644
--- a/ext/sodium/libsodium.c
+++ b/ext/sodium/libsodium.c
@@ -1391,7 +1391,7 @@ PHP_FUNCTION(sodium_crypto_stream_xchacha20_xor_ic)
 		RETURN_THROWS();
 	}
 	if (key_len != crypto_stream_xchacha20_KEYBYTES) {
-		zend_argument_error(sodium_exception_ce, 3, "must be SODIUM_CRYPTO_STREAM_XCHACHA20_KEYBYTES bytes long");
+		zend_argument_error(sodium_exception_ce, 4, "must be SODIUM_CRYPTO_STREAM_XCHACHA20_KEYBYTES bytes long");
 		RETURN_THROWS();
 	}
 	ciphertext_len = msg_len;
diff --git a/ext/sodium/tests/crypto_stream_xchacha20.phpt b/ext/sodium/tests/crypto_stream_xchacha20.phpt
index 466734853d70..08d81b0ed18b 100644
--- a/ext/sodium/tests/crypto_stream_xchacha20.phpt
+++ b/ext/sodium/tests/crypto_stream_xchacha20.phpt
@@ -75,6 +75,11 @@ try {
 } catch (SodiumException $ex) {
     echo $ex->getMessage(), "\n";
 }
+try {
+    sodium_crypto_stream_xchacha20_xor_ic($stream, $nonce, 0, substr($key, 1));
+} catch (Throwable $ex) {
+    echo $ex::class, ': ', $ex->getMessage(), "\n";
+}
 
 ?>
 --EXPECT--
@@ -94,3 +99,4 @@ sodium_crypto_stream_xchacha20(): Argument #2 ($nonce) must be SODIUM_CRYPTO_STR
 sodium_crypto_stream_xchacha20(): Argument #3 ($key) must be SODIUM_CRYPTO_STREAM_XCHACHA20_KEYBYTES bytes long
 sodium_crypto_stream_xchacha20_xor(): Argument #2 ($nonce) must be SODIUM_CRYPTO_STREAM_XCHACHA20_NONCEBYTES bytes long
 sodium_crypto_stream_xchacha20_xor(): Argument #3 ($key) must be SODIUM_CRYPTO_STREAM_XCHACHA20_KEYBYTES bytes long
+SodiumException: sodium_crypto_stream_xchacha20_xor_ic(): Argument #4 ($key) must be SODIUM_CRYPTO_STREAM_XCHACHA20_KEYBYTES bytes long