diff --git a/src/calibre/utils/fonts/sfnt/cmap.py b/src/calibre/utils/fonts/sfnt/cmap.py
index 76854863ef..94c13e0f68 100644
--- a/src/calibre/utils/fonts/sfnt/cmap.py
+++ b/src/calibre/utils/fonts/sfnt/cmap.py
@@ -141,7 +141,7 @@ class BMPTable(object):
                             glyph_id = self.glyph_id_map[idx]
                             if glyph_id != 0:
                                 glyph_id += self.id_delta[i]
-                        yield glyph_id % 0x1000
+                        yield glyph_id % 0x10000
                         break
             if not found:
                 yield 0
@@ -159,7 +159,7 @@ class BMPTable(object):
                     glyph_id = self.glyph_id_map[idx]
                     if glyph_id != 0:
                         glyph_id += self.id_delta[i]
-                glyph_id %= 0x1000
+                glyph_id %= 0x10000
                 if glyph_id in glyph_ids and code not in ans:
                     ans[code] = glyph_id
         return ans
diff --git a/src/calibre/utils/fonts/utils.py b/src/calibre/utils/fonts/utils.py
index ec88dacae3..7678503e7f 100644
--- a/src/calibre/utils/fonts/utils.py
+++ b/src/calibre/utils/fonts/utils.py
@@ -350,7 +350,7 @@ def get_bmp_glyph_ids(table, bmp, codes):
                         glyph_id = glyph_id_map[idx]
                         if glyph_id != 0:
                             glyph_id += id_delta[i]
-                    yield glyph_id % 0x1000
+                    yield glyph_id % 0x10000
                     break
         if not found:
             yield 0