diff --git a/ext/standard/pack.c b/ext/standard/pack.c
index c8cbf8613f63..969f5a2db742 100644
--- a/ext/standard/pack.c
+++ b/ext/standard/pack.c
@@ -803,7 +803,7 @@ PHP_FUNCTION(unpack)
 
 
 	if (offset < 0 || offset > inputlen) {
-		zend_argument_value_error(3, "must be contained in argument #2 ($data)");
+		zend_argument_value_error(3, "must be contained in argument #2 ($string)");
 		RETURN_THROWS();
 	}
 
diff --git a/ext/standard/tests/strings/unpack_offset.phpt b/ext/standard/tests/strings/unpack_offset.phpt
index a3046c32d6f9..36d3f49eb495 100644
--- a/ext/standard/tests/strings/unpack_offset.phpt
+++ b/ext/standard/tests/strings/unpack_offset.phpt
@@ -21,9 +21,17 @@ try {
 } catch (Throwable $e) {
     echo $e::class, ': ', $e->getMessage(), "\n";
 }
+
+/* the message names argument #2, so that name has to be the real one */
+foreach ((new ReflectionFunction('unpack'))->getParameters() as $parameter) {
+    echo '$', $parameter->getName(), "\n";
+}
 ?>
 --EXPECT--
 0x01020304 0x05060708
 0x01020304 0x05060708
-ValueError: unpack(): Argument #3 ($offset) must be contained in argument #2 ($data)
-ValueError: unpack(): Argument #3 ($offset) must be contained in argument #2 ($data)
+ValueError: unpack(): Argument #3 ($offset) must be contained in argument #2 ($string)
+ValueError: unpack(): Argument #3 ($offset) must be contained in argument #2 ($string)
+$format
+$string
+$offset