diff --git a/cmake/modules/LLVMProcessSources.cmake b/cmake/modules/LLVMProcessSources.cmake
index 12a8968c724..b753735cd55 100644
--- a/cmake/modules/LLVMProcessSources.cmake
+++ b/cmake/modules/LLVMProcessSources.cmake
@@ -22,6 +22,7 @@ endmacro(add_header_files)
 
 function(llvm_process_sources OUT_VAR)
   set( sources ${ARGN} )
+  llvm_check_source_file_list( ${sources} )
   # Create file dependencies on the tablegenned files, if any.  Seems
   # that this is not strictly needed, as dependencies of the .cpp
   # sources on the tablegenned .inc files are detected and handled,
@@ -37,3 +38,17 @@ function(llvm_process_sources OUT_VAR)
   endif()
   set( ${OUT_VAR} ${sources} PARENT_SCOPE )
 endfunction(llvm_process_sources)
+
+
+function(llvm_check_source_file_list)
+  set(listed ${ARGN})
+  file(GLOB globbed *.cpp)
+  foreach(g ${globbed})
+    get_filename_component(fn ${g} NAME)
+    list(FIND listed ${fn} idx)
+    if( idx LESS 0 )
+      message(SEND_ERROR "Found unknown source file ${g}
+Please update ${CMAKE_CURRENT_SOURCE_DIR}/CMakeLists.txt\n")
+    endif()
+  endforeach()
+endfunction(llvm_check_source_file_list)