diff --git a/crypto/mbedtls/CMakeLists.txt b/crypto/mbedtls/CMakeLists.txt
index 9d9561814..03bf85316 100644
--- a/crypto/mbedtls/CMakeLists.txt
+++ b/crypto/mbedtls/CMakeLists.txt
@@ -77,7 +77,7 @@ if(CONFIG_CRYPTO_MBEDTLS)
   nuttx_export_header(TARGET mbedtls INCLUDE_DIRECTORIES ${MBEDTLS_DIR}/include)
   target_sources(mbedtls PRIVATE ${CSRCS})
   target_include_directories(mbedtls PRIVATE ${INCDIR})
-  target_compile_definitions(mbedtls PRIVATE __unix__)
+  target_compile_definitions(mbedtls PRIVATE unix)
 
   if(CONFIG_ARCH_SIM)
     target_compile_options(mbedtls PRIVATE -O0)
diff --git a/crypto/mbedtls/Makefile b/crypto/mbedtls/Makefile
index 400259dcd..bb79154c3 100644
--- a/crypto/mbedtls/Makefile
+++ b/crypto/mbedtls/Makefile
@@ -36,7 +36,7 @@ MBEDTLS_UNPACKLIBDIR = $(MBEDTLS_UNPACKNAME)$(DELIM)library
 MBEDTLS_UNPACKPROGDIR = $(MBEDTLS_UNPACKNAME)$(DELIM)programs
 
 # This lets Mbed TLS better use some of the POSIX features we have
-CFLAGS += ${DEFINE_PREFIX}__unix__
+CFLAGS += ${DEFINE_PREFIX}unix
 
 mbedtls/library/bignum.c_CFLAGS += -fno-lto