diff --git a/External/SPEC/CFP2017rate/526.blender_r/CMakeLists.txt b/External/SPEC/CFP2017rate/526.blender_r/CMakeLists.txt
index e063991..4c7aeca 100644
--- a/External/SPEC/CFP2017rate/526.blender_r/CMakeLists.txt
+++ b/External/SPEC/CFP2017rate/526.blender_r/CMakeLists.txt
@@ -15,6 +15,7 @@
   -DHAVE_UNSIGNED_CHAR
 )
 add_compile_options(-funsigned-char)
+add_compile_options($<$<COMPILE_LANGUAGE:CXX>:-D__BOOL_DEFINED>)
 speccpu2017_add_include_dirs(
   specrand
   blender/extern/binreloc/include