diff --git a/options/posix/generic/unistd-stubs.cpp b/options/posix/generic/unistd-stubs.cpp
index 16ab8b74f9..d69c83bef2 100644
--- a/options/posix/generic/unistd-stubs.cpp
+++ b/options/posix/generic/unistd-stubs.cpp
@@ -666,9 +666,15 @@ int setuid(uid_t uid) {
 	return 0;
 }
 
-void swab(const void *__restrict, void *__restrict, ssize_t) {
-	__ensure(!"Not implemented");
-	__builtin_unreachable();
+void swab(const void *_src, void *_dest, ssize_t n) {
+	const char *src = reinterpret_cast<const char *>(_src);
+	char *dest = reinterpret_cast<char *>(_dest);
+	for(; n > 1; n -= 2) {
+		dest[0] = src[1];
+		dest[1] = src[0];
+		dest += 2;
+		src += 2;
+	}
 }
 
 int symlink(const char *target_path, const char *link_path) {
diff --git a/options/posix/include/unistd.h b/options/posix/include/unistd.h
index 627f33a660..45789b4156 100644
--- a/options/posix/include/unistd.h
+++ b/options/posix/include/unistd.h
@@ -330,7 +330,7 @@ pid_t setsid(void);
 int setuid(uid_t);
 void setusershell(void);
 unsigned int sleep(unsigned int);
-void swab(const void *__restrict, void *__restrict, ssize_t);
+void swab(const void *_src, void *_dest, ssize_t n);
 int symlink(const char *, const char *);
 int symlinkat(const char *, int, const char *);
 void sync(void);