diff --git a/include/wb/DataValueQuantity.php b/include/wb/DataValueQuantity.php
--- a/include/wb/DataValueQuantity.php
+++ b/include/wb/DataValueQuantity.php
@@ -1,6 +1,7 @@
 <?php
 # Boz-MW - Another MediaWiki API handler in PHP
-# Copyright (C) 2018 Valerio Bozzolan
+# Copyright (C) 2018-2023 Valerio Bozzolan
+# Copyright (C) 2023      Luca Mauri
 #
 # This program is free software: you can redistribute it and/or modify
 # it under the terms of the GNU Affero General Public License as published by
@@ -30,10 +31,16 @@
 	 * @param $lower_bound mixed The $value at its minimum error e.g. -1
 	 */
 	public function __construct( $amount, $wikidata_unit_id, $upper_bound = null, $lower_bound = null ) {
-		$value = [
-			'amount' => self::sign( $amount ),
-			'unit'   => "http://www.wikidata.org/entity/$wikidata_unit_id"
-		];
+		$value = [];
+
+		// if the Wikidata unit ID is not specified, just "1"
+		// if that is NOT a Q-ID, just "1" too
+		if (($wikidata_unit_id === null) || (strtoupper(substr($wikidata_unit_id, 0, 1)) !== 'Q')) {
+			$value['unit'] = '1';
+		} else {
+			$value['unit'] = "http://www.wikidata.org/entity/$wikidata_unit_id";
+		}
+
 		if( null !== $upper_bound ) {
 			$value['upperBound'] = self::int2string( $upper_bound );
 		}
diff --git a/include/wb/SnakQuantity.php b/include/wb/SnakQuantity.php
--- a/include/wb/SnakQuantity.php
+++ b/include/wb/SnakQuantity.php
@@ -1,6 +1,7 @@
 <?php
 # Boz-MW - Another MediaWiki API handler in PHP
-# Copyright (C) 2018 Valerio Bozzolan
+# Copyright (C) 2018-2023 Valerio Bozzolan
+# Copyright (C) 2023      Luca Mauri
 #
 # This program is free software: you can redistribute it and/or modify
 # it under the terms of the GNU Affero General Public License as published by
@@ -24,8 +25,11 @@
 class SnakQuantity extends Snak {
 
 	/**
-	 * @param $property string Wikidata property as 'P123'
-	 * @param $value    string
+	 * @param $property string Property as 'P123'
+	 * @param $value mixed amount Any number e.g. 0
+	 * @param $wikidata_unit_id string Wikidata ID of a unit e.g. 'Q11573' for metre
+	 * @param $upper_bound mixed The $value at its maximum error e.g. +1
+	 * @param $lower_bound mixed The $value at its minimum error e.g. -1
 	 */
 	public function __construct( $property, $amount, $unit, $upper_bound = null, $lower_bound = null ) {
 		return parent::__construct(
diff --git a/include/wb/StatementQuantity.php b/include/wb/StatementQuantity.php
--- a/include/wb/StatementQuantity.php
+++ b/include/wb/StatementQuantity.php
@@ -1,6 +1,7 @@
 <?php
 # Boz-MW - Another MediaWiki API handler in PHP
-# Copyright (C) 2018 Valerio Bozzolan
+# Copyright (C) 2018-2023 Valerio Bozzolan
+# Copyright (C) 2023      Luca Mauri
 #
 # This program is free software: you can redistribute it and/or modify
 # it under the terms of the GNU Affero General Public License as published by
@@ -19,7 +20,7 @@
 namespace wb;
 
 /**
- * A StatementString is a Statement that contains a SnakString.
+ * A StatementQuantity is a Statement that contains a SnakQuantity.
  */
 class StatementQuantity extends Statement {