diff --git a/src/calibre/utils/filenames.py b/src/calibre/utils/filenames.py
index 678b751fac..e821b4af66 100644
--- a/src/calibre/utils/filenames.py
+++ b/src/calibre/utils/filenames.py
@@ -338,8 +338,8 @@ def windows_hardlink(src, dest):
 
     sz = windows_get_size(dest)
     if sz != src_size:
-        msg = f'Creating hardlink from {src} to {dest} failed: %s'
-        raise OSError(msg % ('hardlink size: %d not the same as source size' % sz))
+        msg = f'Creating hardlink from {src} to {dest} failed: '
+        raise OSError(msg + (f'hardlink size: {sz} not the same as source size'))
 
 
 def windows_fast_hardlink(src, dest):
@@ -347,8 +347,8 @@ def windows_fast_hardlink(src, dest):
     winutil.create_hard_link(dest, src)
     ssz, dsz = windows_get_size(src), windows_get_size(dest)
     if ssz != dsz:
-        msg = f'Creating hardlink from {src} to {dest} failed: %s'
-        raise OSError(msg % ('hardlink size: %d not the same as source size: %s' % (dsz, ssz)))
+        msg = f'Creating hardlink from {src} to {dest} failed: '
+        raise OSError(msg + (f'hardlink size: {dsz} not the same as source size: {ssz}'))
 
 
 def windows_nlinks(path):