diff --git a/tools/services/check_service.py b/tools/services/check_service.py
index dc3b975..442d840 100644
--- a/tools/services/check_service.py
+++ b/tools/services/check_service.py
@@ -32,11 +32,12 @@ def check_glyph_files(font_config: FontConfig):
                 block = unidata_blocks.get_block_by_code_point(code_point)
                 east_asian_width = unicodedata.east_asian_width(chr(code_point))
 
-            bitmap_strings = set()
+            bitmap_strings = {}
             for glyph_file in set(flavor_group.values()):
                 bitmap_string = str(glyph_file.bitmap)
-                assert bitmap_string not in bitmap_strings, f"[{font_config.font_size}px] duplicate glyph bitmaps: '{glyph_file.file_path}'"
-                bitmap_strings.add(bitmap_string)
+                duplicate_glyph_file = bitmap_strings.get(bitmap_string, None)
+                assert duplicate_glyph_file is None, f"[{font_config.font_size}px] duplicate glyph bitmaps:\n'{glyph_file.file_path}'\n'{duplicate_glyph_file.file_path}'"
+                bitmap_strings[bitmap_string] = glyph_file
 
                 if width_mode_dir_name == 'common' or width_mode_dir_name == 'monospaced':
                     assert glyph_file.height == font_config.font_size, f"[{font_config.font_size}px] glyph bitmap error: '{glyph_file.file_path}'"