diff --git a/lib/avro/datum.php b/lib/avro/datum.php
index 8e74252..c4499e0 100644
--- a/lib/avro/datum.php
+++ b/lib/avro/datum.php
@@ -242,7 +242,7 @@ private function write_map($writers_schema, $datum, $encoder)
       $encoder->write_long($datum_count);
       foreach ($datum as $k => $v)
       {
-        $encoder->write_string($k);
+        $encoder->write_string((string) $k);
         $this->write_data($writers_schema->values(), $v, $encoder);
       }
     }
diff --git a/lib/avro/schema.php b/lib/avro/schema.php
index 89b0de0..745a973 100644
--- a/lib/avro/schema.php
+++ b/lib/avro/schema.php
@@ -446,7 +446,7 @@ public static function is_valid_datum($expected_schema, $datum)
         if (is_array($datum))
         {
           foreach ($datum as $k => $v)
-            if (!is_string($k)
+            if ((!is_string($k) && !is_int($k))
                 || !self::is_valid_datum($expected_schema->values(), $v))
               return false;
           return true;
diff --git a/test/DatumIOTest.php b/test/DatumIOTest.php
index c9018af..b6ac9aa 100644
--- a/test/DatumIOTest.php
+++ b/test/DatumIOTest.php
@@ -135,6 +135,9 @@ function data_provider()
                  array('{"type":"map","values":"int"}',
                        array('foo' => 1, 'bar' => 2, 'baz' => 3),
                        "\x06\x06foo\x02\x06bar\x04\x06baz\x06\x00"),
+                 array('{"type":"map","values":"int"}',
+                       array('123' => 1, 456 => 2, 'foo' => 3),
+                       "\x06\x06123\x02\x06456\x04\x06foo\x06\x00"),
                  array('["null", "int"]', 1, "\x02\x02"),
                  array('{"name":"fix","type":"fixed","size":3}',
                        "\xAA\xBB\xCC", "\xAA\xBB\xCC"),