diff --git a/src/ocrmypdf/helpers.py b/src/ocrmypdf/helpers.py
index 3a2c9051..afd8eaa7 100644
--- a/src/ocrmypdf/helpers.py
+++ b/src/ocrmypdf/helpers.py
@@ -216,10 +216,7 @@ def check_pdf(input_file: Path) -> bool:
             pdf.close()
 
 
-T = TypeVar('T')
-
-
-def clamp(n: T, smallest: T, largest: T) -> T:
+def clamp(n, smallest, largest):  # mypy doesn't understand types for this
     """Clamps the value of n to between smallest and largest."""
     return max(smallest, min(n, largest))
 
@@ -232,6 +229,7 @@ def pikepdf_enable_mmap():
     #     log.debug("pikepdf mmap not available")
     # We found a race condition probably related to pybind issue #2252 that can
     # cause a crash. For now, disable pikepdf mmap to be on the safe side.
+    # Fix is not in pybind11 2.6.0
     log.debug("pikepdf mmap disabled")
     return
 
diff --git a/src/ocrmypdf/optimize.py b/src/ocrmypdf/optimize.py
index cc9c8318..9fd80db7 100644
--- a/src/ocrmypdf/optimize.py
+++ b/src/ocrmypdf/optimize.py
@@ -25,7 +25,6 @@ from typing import (
     Optional,
     Sequence,
     Tuple,
-    Union,
 )
 
 import img2pdf
@@ -294,10 +293,6 @@ def extract_images_jbig2(pike: Pdf, root: Path, options) -> Dict[int, List[XrefE
         group = pageno // options.jbig2_page_group_size
         jbig2_groups[group].append(xref_ext)
 
-    # Elide empty groups
-    jbig2_groups = {
-        group: xrefs for group, xrefs in jbig2_groups.items() if len(xrefs) > 0
-    }
     log.debug("Optimizable images: JBIG2 groups: %s", (len(jbig2_groups),))
     return jbig2_groups