diff --git a/flang/tools/f18/CMakeLists.txt b/flang/tools/f18/CMakeLists.txt
--- a/flang/tools/f18/CMakeLists.txt
+++ b/flang/tools/f18/CMakeLists.txt
@@ -45,8 +45,10 @@
 
 # This flang shell script will only work in a POSIX shell.
 if (NOT WIN32)
-  file(COPY ${CMAKE_CURRENT_SOURCE_DIR}/flang
-    DESTINATION ${CMAKE_BINARY_DIR}/bin
-    FILE_PERMISSIONS OWNER_EXECUTE OWNER_READ OWNER_WRITE)
+  add_custom_command(
+    OUTPUT ${CMAKE_BINARY_DIR}/bin/flang
+    DEPENDS ${CMAKE_CURRENT_SOURCE_DIR}/flang
+    COMMAND ${CMAKE_COMMAND} -E copy ${CMAKE_CURRENT_SOURCE_DIR}/flang ${CMAKE_BINARY_DIR}/bin)
+  add_custom_target(flang ALL DEPENDS ${CMAKE_BINARY_DIR}/bin/flang)
   install(PROGRAMS ${CMAKE_BINARY_DIR}/bin/flang DESTINATION "${CMAKE_INSTALL_BINDIR}")
 endif()