diff --git a/tinycbor/open_memstream.c b/tinycbor/open_memstream.c
index 3365378..37a0d08 100644
--- a/tinycbor/open_memstream.c
+++ b/tinycbor/open_memstream.c
@@ -32,13 +32,13 @@
 #include <stdlib.h>
 #include <string.h>

-#if defined(__unix__) || defined(__APPLE__)
+#if defined(__unix__) || defined(__APPLE__) || defined(__NuttX__)
 #  include <unistd.h>
 #endif
-#ifdef __APPLE__
+#if defined(__APPLE__)
 typedef int RetType;
 typedef int LenType;
-#elif __linux__
+#elif defined(__linux__) || defined(__NuttX__)
 typedef ssize_t RetType;
 typedef size_t LenType;
 #else
@@ -99,9 +99,9 @@ FILE *open_memstream(char **bufptr, size_t *lenptr)
     *bufptr = NULL;
     *lenptr = 0;

-#ifdef __APPLE__
+#if defined(__APPLE__)
     return funopen(b, NULL, write_to_buffer, NULL, close_buffer);
-#elif __linux__
+#elif defined(__linux__) || defined(__NuttX__)
     static const cookie_io_functions_t vtable = {
         NULL,
         write_to_buffer,