diff --git a/src/calibre/utils/fonts/sfnt/merge.py b/src/calibre/utils/fonts/sfnt/merge.py
index 986e72ae62..1da10537fd 100644
--- a/src/calibre/utils/fonts/sfnt/merge.py
+++ b/src/calibre/utils/fonts/sfnt/merge.py
@@ -27,7 +27,7 @@ def merge_truetype_fonts_for_pdf(*fonts):
                 if prev_glyph_data is None:
                     all_glyphs[glyph_id] = glyf.glyph_data(offset, sz, as_raw=True)
                 else:
-                    if abs(sz - len(prev_glyph_data)) > 4:
+                    if abs(sz - len(prev_glyph_data)) > 8:
                         raise GlyphSizeMismatch('Size mismatch for glyph id: {} prev_sz: {} sz: {}'.format(glyph_id, len(prev_glyph_data), sz))
 
     glyf = ans[b'glyf']