diff --git a/src/Map.php b/src/Map.php
index aeaf330..5557502 100644
--- a/src/Map.php
+++ b/src/Map.php
@@ -525,6 +525,8 @@ public function at( int $pos )
 	 * The first line will return "3", the second and third one "2", the forth
 	 * one "30" and the last one "40".
 	 *
+	 * NULL values are treated as 0, non-numeric values will generate an error.
+	 *
 	 * This does also work for multi-dimensional arrays by passing the keys
 	 * of the arrays separated by the delimiter ("/" by default), e.g. "key1/key2/key3"
 	 * to get "val" from ['key1' => ['key2' => ['key3' => 'val']]]. The same applies to
@@ -4661,6 +4663,8 @@ public function suffix( $suffix, int $depth = null ) : self
 	 * The first line will return "9", the second one "6", the third one "90"
 	 * and the last one "80".
 	 *
+	 * NULL values are treated as 0, non-numeric values will generate an error.
+	 *
 	 * This does also work for multi-dimensional arrays by passing the keys
 	 * of the arrays separated by the delimiter ("/" by default), e.g. "key1/key2/key3"
 	 * to get "val" from ['key1' => ['key2' => ['key3' => 'val']]]. The same applies to
diff --git a/tests/MapTest.php b/tests/MapTest.php
index dda829e..f85175a 100644
--- a/tests/MapTest.php
+++ b/tests/MapTest.php
@@ -142,7 +142,7 @@ public function testAvg()
 	{
 		$this->assertSame( 3.0, Map::from( [1, 3, 5] )->avg() );
 		$this->assertSame( 2.0, Map::from( [1, null, 5] )->avg() );
-		$this->assertSame( 2.0, Map::from( [1, 'sum', 5] )->avg() );
+		$this->assertSame( 2.0, Map::from( [1, 0.0, 5] )->avg() );
 	}
 
 
@@ -3070,7 +3070,7 @@ public function testSuffix()
 	public function testSum()
 	{
 		$this->assertSame( 9.0, Map::from( [1, 3, 5] )->sum() );
-		$this->assertSame( 6.0, Map::from( [1, 'sum', 5] )->sum() );
+		$this->assertSame( 6.0, Map::from( [1, 0.0, 5] )->sum() );
 	}