diff --git a/llvm/docs/HowToCrossCompileLLVM.rst b/llvm/docs/HowToCrossCompileLLVM.rst
--- a/llvm/docs/HowToCrossCompileLLVM.rst
+++ b/llvm/docs/HowToCrossCompileLLVM.rst
@@ -40,7 +40,7 @@
 
 The CMake options you need to add are:
 
- * ``-DCMAKE_CROSSCOMPILING=True``
+ * ``-DCMAKE_SYSTEM_NAME=<target-system>``
  * ``-DCMAKE_INSTALL_PREFIX=<install-dir>``
  * ``-DLLVM_TABLEGEN=<path-to-host-bin>/llvm-tblgen``
  * ``-DCLANG_TABLEGEN=<path-to-host-bin>/clang-tblgen``
@@ -48,6 +48,8 @@
  * ``-DLLVM_TARGET_ARCH=ARM``
  * ``-DLLVM_TARGETS_TO_BUILD=ARM``
 
+Note: ``CMAKE_CROSSCOMPILING`` is always set automatically when ``CMAKE_SYSTEM_NAME`` is set. Don't put ``-DCMAKE_CROSSCOMPILING=TRUE`` in your options.
+
 If you're compiling with GCC, you can use architecture options for your target,
 and the compiler driver will detect everything that it needs: