diff --git a/src/system/libroot/posix/math/Jamfile b/src/system/libroot/posix/math/Jamfile
index f2d7796556..f8692c07b8 100644
--- a/src/system/libroot/posix/math/Jamfile
+++ b/src/system/libroot/posix/math/Jamfile
@@ -1,6 +1,7 @@
 SubDir OBOS_TOP src system libroot posix math ;
 
 SubDirHdrs [ FDirName $(SUBDIR) $(DOTDOT) glibc ] ;
+SubDirCcFlags -Dnational ;
 
 KernelMergeObject posix_math.o :
 	acosh.c