diff --git a/pytiled_parser/util.py b/pytiled_parser/util.py
index 089cdace..f33dca63 100644
--- a/pytiled_parser/util.py
+++ b/pytiled_parser/util.py
@@ -39,11 +39,11 @@ def parse_color(color: str) -> Color:
 
 def check_format(file_path: Path, encoding: str) -> str:
     with open(file_path, encoding=encoding) as file:
-        line = file.readline().rstrip().strip()
-        if line[0] == "<":
-            return "tmx"
-        else:
-            return "json"
+        for line in file:
+            line = line.strip()
+            if line:
+                return "tmx" if line.startswith("<") else "json"
+    return "json"
 
 
 def load_object_template(file_path: Path, encoding: str) -> Any:
diff --git a/tests/test_format_detection.py b/tests/test_format_detection.py
new file mode 100644
index 00000000..7657a9e5
--- /dev/null
+++ b/tests/test_format_detection.py
@@ -0,0 +1,48 @@
+import json
+
+import pytest
+
+from pytiled_parser import UnknownFormat, parse_map
+from pytiled_parser.common_types import Size
+
+MAP = {
+    "version": "1.9",
+    "tiledversion": "1.9.1",
+    "orientation": "orthogonal",
+    "renderorder": "right-down",
+    "width": 1,
+    "height": 1,
+    "tilewidth": 16,
+    "tileheight": 16,
+    "infinite": False,
+    "nextlayerid": 1,
+    "nextobjectid": 1,
+    "layers": [],
+    "tilesets": [],
+}
+
+TMX = (
+    '<map version="1.9" tiledversion="1.9.1" orientation="orthogonal" '
+    'renderorder="right-down" width="1" height="1" tilewidth="16" '
+    'tileheight="16" infinite="0" nextlayerid="1" nextobjectid="1"/>'
+)
+
+
+@pytest.mark.parametrize("prefix", ["", "\n", "\r\n\r\n", " \t\n\n"])
+@pytest.mark.parametrize("format_", ["json", "tmx"])
+def test_leading_blank_lines(tmp_path, prefix, format_):
+    map_file = tmp_path / ("map." + format_)
+    content = json.dumps(MAP) if format_ == "json" else TMX
+    map_file.write_text(prefix + content, encoding="utf-8")
+    parsed = parse_map(map_file)
+    assert parsed.map_size == Size(1, 1)
+    assert parsed.tile_size == Size(16, 16)
+    assert parsed.layers == []
+
+
+@pytest.mark.parametrize("content", ["", "\n", " \t\n\r\n"])
+def test_empty_map_has_format_error(tmp_path, content):
+    map_file = tmp_path / "map.json"
+    map_file.write_text(content, encoding="utf-8")
+    with pytest.raises(UnknownFormat):
+        parse_map(map_file)