diff --git a/libcxx/include/__support/ibm/nanosleep.h b/libcxx/include/__support/ibm/nanosleep.h
--- a/libcxx/include/__support/ibm/nanosleep.h
+++ b/libcxx/include/__support/ibm/nanosleep.h
@@ -12,27 +12,42 @@
 
 #include <unistd.h>
 
-inline int nanosleep(const struct timespec* req, struct timespec* rem)
-{
-   // The nanosleep() function is not available on z/OS. Therefore, we will call
-   // sleep() to sleep for whole seconds and usleep() to sleep for any remaining
-   // fraction of a second. Any remaining nanoseconds will round up to the next
-   // microsecond.
-
-   useconds_t __micro_sec = (rem->tv_nsec + 999) / 1000;
-   if (__micro_sec > 999999)
-   {
-     ++rem->tv_sec;
-     __micro_sec -= 1000000;
-   }
-   while (rem->tv_sec)
-      rem->tv_sec = sleep(rem->tv_sec);
-   if (__micro_sec) {
-     rem->tv_nsec = __micro_sec * 1000;
-     return usleep(__micro_sec);
-   }
-   rem->tv_nsec = 0;
-   return 0;
+inline int nanosleep(const struct timespec* __req, struct timespec* __rem) {
+  // The nanosleep() function is not available on z/OS. Therefore, we will call
+  // sleep() to sleep for whole seconds and usleep() to sleep for any remaining
+  // fraction of a second. Any remaining nanoseconds will round up to the next
+  // microsecond.
+  if (__req->tv_sec < 0 || __req->tv_nsec < 0 || __req->tv_nsec > 999999999) {
+    errno = EINVAL;
+    return -1;
+  }
+  useconds_t __micro_sec =
+      static_cast<useconds_t>((__req->tv_nsec + 999) / 1000);
+  time_t __sec = __req->tv_sec;
+  if (__micro_sec > 999999) {
+    ++__sec;
+    __micro_sec -= 1000000;
+  }
+  __sec = sleep(static_cast<unsigned int>(__sec));
+  if (__sec) {
+    if (__rem) {
+      __rem->tv_sec = __sec;
+      __rem->tv_nsec = __micro_sec * 1000;
+    }
+    errno = EINTR;
+    return -1;
+  }
+  if (__micro_sec) {
+    int rc = usleep(__micro_sec);
+    if (rc != 0 && __rem) {
+      __rem->tv_sec = 0;
+      __rem->tv_nsec = __micro_sec * 1000;
+      // errno is already set
+      return -1;
+    }
+    return rc;
+  }
+  return 0;
 }
 
 #endif // _LIBCPP_SUPPORT_IBM_NANOSLEEP_H