diff --git a/src/unix/os390-syscalls.c b/src/unix/os390-syscalls.c
index 190ff1be..53dca91f 100644
--- a/src/unix/os390-syscalls.c
+++ b/src/unix/os390-syscalls.c
@@ -556,3 +556,28 @@ size_t strnlen(const char* str, size_t maxlen) {
   else
     return p - str;
 }
+
+
+int sem_init(UV_PLATFORM_SEM_T* semid, int pshared, unsigned int value) {
+  UNREACHABLE();
+}
+
+
+int sem_destroy(UV_PLATFORM_SEM_T* semid) {
+  UNREACHABLE();
+}
+
+
+int sem_post(UV_PLATFORM_SEM_T* semid) {
+  UNREACHABLE();
+}
+
+
+int sem_trywait(UV_PLATFORM_SEM_T* semid) {
+  UNREACHABLE();
+}
+
+
+int sem_wait(UV_PLATFORM_SEM_T* semid) {
+  UNREACHABLE();
+}
diff --git a/src/unix/os390-syscalls.h b/src/unix/os390-syscalls.h
index 5130457c..86416bbc 100644
--- a/src/unix/os390-syscalls.h
+++ b/src/unix/os390-syscalls.h
@@ -65,5 +65,10 @@ int scandir(const char* maindir, struct dirent*** namelist,
 char *mkdtemp(char* path);
 ssize_t os390_readlink(const char* path, char* buf, size_t len);
 size_t strnlen(const char* str, size_t maxlen);
+int sem_init(UV_PLATFORM_SEM_T* semid, int pshared, unsigned int value);
+int sem_destroy(UV_PLATFORM_SEM_T* semid);
+int sem_post(UV_PLATFORM_SEM_T* semid);
+int sem_trywait(UV_PLATFORM_SEM_T* semid);
+int sem_wait(UV_PLATFORM_SEM_T* semid);
 
 #endif /* UV_OS390_SYSCALL_H_ */