diff --git a/boards/sim/sim/sim/scripts/Make.defs b/boards/sim/sim/sim/scripts/Make.defs
index c91161b97a..691f14d301 100644
--- a/boards/sim/sim/sim/scripts/Make.defs
+++ b/boards/sim/sim/sim/scripts/Make.defs
@@ -75,7 +75,7 @@ OBJDUMP = $(CROSSDEV)objdump
 CFLAGS := $(ARCHWARNINGS) $(ARCHOPTIMIZATION) \
    $(ARCHCPUFLAGS) $(ARCHINCLUDES) $(ARCHDEFINES) $(EXTRAFLAGS) -pipe
 CXXFLAGS := $(ARCHWARNINGSXX) $(ARCHOPTIMIZATION) \
-   $(ARCHCPUFLAGSXX) $(ARCHXXINCLUDES) $(ARCHDEFINESXX) $(EXTRAFLAGS) -pipe
+   $(ARCHCPUFLAGSXX) $(ARCHXXINCLUDES) $(ARCHDEFINES) $(EXTRAFLAGS) -pipe
 CPPFLAGS := $(ARCHINCLUDES) $(ARCHDEFINES) $(EXTRAFLAGS)
 AFLAGS := $(CFLAGS) -D__ASSEMBLY__