diff --git a/doc/bugs/filecheck.pm:_warnings_about_division_with_uninitialized_value.mdwn b/doc/bugs/filecheck.pm:_warnings_about_division_with_uninitialized_value.mdwn
new file mode 100644
index 000000000..dff77a00d
--- /dev/null
+++ b/doc/bugs/filecheck.pm:_warnings_about_division_with_uninitialized_value.mdwn
@@ -0,0 +1,20 @@
+If you enable [[plugins/filecheck]] *and* [[plugins/attachment]], then IkiWiki (e.g. via wrapper) will throw a lot of the following errors on stderr
+
+    Use of uninitialized value $size in division (/) at /.../filecheck.pm line 73.
+
+73 is
+
+```
+sub humansize ($) {
+	my $size=shift;
+
+	foreach my $unit (reverse sort { $units{$a} <=> $units{$b} || $b cmp $a } keys %units) {
+		if ($size / $units{$unit} > 0.25) {
+			return (int($size / $units{$unit} * 10)/10).$unit;
+		}
+	}
+	return $size; # near zero, or negative
+}
+```
+
+Disabling *attachment* is sufficient to stop this. *&mdash; [[Jon]] 2023-09-06*