diff --git a/boards/sim/sim/sim/scripts/Make.defs b/boards/sim/sim/sim/scripts/Make.defs
index d2d1e7cb29e..b14330f21de 100644
--- a/boards/sim/sim/sim/scripts/Make.defs
+++ b/boards/sim/sim/sim/scripts/Make.defs
@@ -98,13 +98,10 @@ OBJDUMP = $(CROSSDEV)objdump
 # Note: -fshort-wchar for the case where NuttX and the host OS have
 # different wchar_t. On NuttX, it's uint16_t. On macOS, it's 32-bit.
 CFLAGS := $(ARCHWARNINGS) $(ARCHOPTIMIZATION) \
-   $(ARCHCPUFLAGS) $(ARCHINCLUDES) $(ARCHDEFINES) $(EXTRAFLAGS) -pipe \
-   -fshort-wchar
+   $(ARCHCPUFLAGS) $(ARCHINCLUDES) $(ARCHDEFINES) $(EXTRAFLAGS) -pipe
 CXXFLAGS := $(ARCHWARNINGSXX) $(ARCHOPTIMIZATION) \
-   $(ARCHCPUFLAGSXX) $(ARCHXXINCLUDES) $(ARCHDEFINES) $(EXTRAFLAGS) -pipe \
-   -fshort-wchar
-CPPFLAGS := $(ARCHINCLUDES) $(ARCHDEFINES) $(EXTRAFLAGS) \
-   -fshort-wchar
+   $(ARCHCPUFLAGSXX) $(ARCHXXINCLUDES) $(ARCHDEFINES) $(EXTRAFLAGS) -pipe
+CPPFLAGS := $(ARCHINCLUDES) $(ARCHDEFINES) $(EXTRAFLAGS)
 AFLAGS := $(CFLAGS) -D__ASSEMBLY__
 
 ifeq ($(CONFIG_LIBCXX),y)
@@ -117,16 +114,6 @@ ifeq ($(CONFIG_LIBCXX),y)
   #    (boards/arm/stm32l4/nucleo-l476rg/scripts/Make.defs)
   #  * libs/libxx/libcxx/src/barrier.cpp depends on aligned new
   CXXFLAGS += -std=c++17
-
-  ifeq ($(CONFIG_HOST_MACOS),y)
-    # macOS uses libc++abi
-    CXXFLAGS += -DLIBCXX_BUILDING_LIBCXXABI
-  else
-    # Linux C++ ABI seems vary.
-    # Probably __GLIBCXX__ is the best bet.
-    # XXX what to do for windows?
-    CXXFLAGS += -D__GLIBCXX__
-  endif
 endif
 
 # Loadable module definitions