diff --git a/llvm/docs/CommandGuide/llvm-objcopy.rst b/llvm/docs/CommandGuide/llvm-objcopy.rst
index 56c3a77..063300a 100644
--- a/llvm/docs/CommandGuide/llvm-objcopy.rst
+++ b/llvm/docs/CommandGuide/llvm-objcopy.rst
@@ -72,6 +72,9 @@
  Remove all sections from the output, except for sections named ``<section>``.
  Can be specified multiple times to keep multiple sections.
 
+ For MachO objects, ``<section>`` must be formatted as
+ ``<segment name>,<section name>``.
+
 .. option:: --regex
 
  If specified, symbol and section names specified by other switches are treated