diff --git a/CMakeLists.txt b/CMakeLists.txt
index 872addd..fb9e2bf 100644
--- a/CMakeLists.txt
+++ b/CMakeLists.txt
@@ -56,6 +56,7 @@
 set(LIBCXX_LIBDIR_SUFFIX "${LLVM_LIBDIR_SUFFIX}" CACHE STRING
     "Define suffix of library directory name (32/64)")
 option(LIBCXX_INSTALL_HEADERS "Install the libc++ headers." ON)
+option(LIBCXX_INSTALL_LIBRARY "Install the libc++ library." ON)
 option(LIBCXX_INSTALL_SUPPORT_HEADERS "Install libc++ support headers." ON)
 
 # ABI Library options ---------------------------------------------------------
@@ -95,6 +96,23 @@
 set(LIBCXX_COVERAGE_LIBRARY "" CACHE STRING
     "The Profile-rt library used to build with code coverage")
 
+# Don't allow a user to accidentally overwrite the system libc++ installation on Darwin.
+# If the user specifies -DCMAKE_INSTALL_PREFIX=/usr the install rules for libc++
+# will not be generated and a warning will be issued.
+option(LIBCXX_OVERRIDE_DARWIN_INSTALL "Enable overwriting darwins libc++ installation." OFF)
+mark_as_advanced(LIBCXX_OVERRIDE_DARWIN_INSTALL) # Don't show this option by default.
+
+if (${CMAKE_SYSTEM_NAME} MATCHES "Darwin" AND NOT LIBCXX_OVERRIDE_DARWIN_INSTALL)
+  if ("${CMAKE_INSTALL_PREFIX}" STREQUAL "/usr")
+    message(WARNING "Disabling libc++ install rules because installation would "
+                    "overwrite the systems installation. Configure with "
+                    "-DLIBCXX_OVERRIDE_DARWIN_INSTALL=ON to suppress this behaviour.")
+    mark_as_advanced(CLEAR LIBCXX_OVERRIDE_DARWIN_INSTALL) # Show the override option.
+    set(LIBCXX_INSTALL_HEADERS OFF)
+    set(LIBCXX_INSTALL_LIBRARY OFF)
+  endif()
+endif()
+
 #===============================================================================
 # Check option configurations
 #===============================================================================