diff --git a/qga/commands-posix.c b/qga/commands-posix.c
index cae4171..9188560 100644
--- a/qga/commands-posix.c
+++ b/qga/commands-posix.c
@@ -142,7 +142,7 @@
    return time_ns;
 }
 
-void qmp_guest_set_time(int64_t time_ns, Error **errp)
+void qmp_guest_set_time(bool has_time, int64_t time_ns, Error **errp)
 {
     int ret;
     int status;
@@ -150,22 +150,28 @@
     Error *local_err = NULL;
     struct timeval tv;
 
-    /* year-2038 will overflow in case time_t is 32bit */
-    if (time_ns / 1000000000 != (time_t)(time_ns / 1000000000)) {
-        error_setg(errp, "Time %" PRId64 " is too large", time_ns);
-        return;
+    /* If user has passed a time, validate and set it. */
+    if (has_time) {
+        /* year-2038 will overflow in case time_t is 32bit */
+        if (time_ns / 1000000000 != (time_t)(time_ns / 1000000000)) {
+            error_setg(errp, "Time %" PRId64 " is too large", time_ns);
+            return;
+        }
+
+        tv.tv_sec = time_ns / 1000000000;
+        tv.tv_usec = (time_ns % 1000000000) / 1000;
+
+        ret = settimeofday(&tv, NULL);
+        if (ret < 0) {
+            error_setg_errno(errp, errno, "Failed to set time to guest");
+            return;
+        }
     }
 
-    tv.tv_sec = time_ns / 1000000000;
-    tv.tv_usec = (time_ns % 1000000000) / 1000;
-
-    ret = settimeofday(&tv, NULL);
-    if (ret < 0) {
-        error_setg_errno(errp, errno, "Failed to set time to guest");
-        return;
-    }
-
-    /* Set the Hardware Clock to the current System Time. */
+    /* Now, if user has passed a time to set and the system time is set, we
+     * just need to synchronize the hardware clock. However, if no time was
+     * passed, user is requesting the opposite: set the system time from the
+     * hardware clock. */
     pid = fork();
     if (pid == 0) {
         setsid();
@@ -173,7 +179,10 @@
         reopen_fd_to_null(1);
         reopen_fd_to_null(2);
 
-        execle("/sbin/hwclock", "hwclock", "-w", NULL, environ);
+        /* Use '/sbin/hwclock -w' to set RTC from the system time,
+         * or '/sbin/hwclock -s' to set the system time from RTC. */
+        execle("/sbin/hwclock", "hwclock", has_time ? "-w" : "-s",
+               NULL, environ);
         _exit(EXIT_FAILURE);
     } else if (pid < 0) {
         error_setg_errno(errp, errno, "failed to create child process");
diff --git a/qga/commands-win32.c b/qga/commands-win32.c
index 50094dd..0ee07b6 100644
--- a/qga/commands-win32.c
+++ b/qga/commands-win32.c
@@ -370,25 +370,37 @@
     return time_ns;
 }
 
-void qmp_guest_set_time(int64_t time_ns, Error **errp)
+void qmp_guest_set_time(bool has_time, int64_t time_ns, Error **errp)
 {
     SYSTEMTIME ts;
     FILETIME tf;
     LONGLONG time;
 
-    if (time_ns < 0 || time_ns / 100 > INT64_MAX - W32_FT_OFFSET) {
-        error_setg(errp, "Time %" PRId64 "is invalid", time_ns);
-        return;
-    }
+    if (has_time) {
+        /* Okay, user passed a time to set. Validate it. */
+        if (time_ns < 0 || time_ns / 100 > INT64_MAX - W32_FT_OFFSET) {
+            error_setg(errp, "Time %" PRId64 "is invalid", time_ns);
+            return;
+        }
 
-    time = time_ns / 100 + W32_FT_OFFSET;
+        time = time_ns / 100 + W32_FT_OFFSET;
 
-    tf.dwLowDateTime = (DWORD) time;
-    tf.dwHighDateTime = (DWORD) (time >> 32);
+        tf.dwLowDateTime = (DWORD) time;
+        tf.dwHighDateTime = (DWORD) (time >> 32);
 
-    if (!FileTimeToSystemTime(&tf, &ts)) {
-        error_setg(errp, "Failed to convert system time %d", (int)GetLastError());
-        return;
+        if (!FileTimeToSystemTime(&tf, &ts)) {
+            error_setg(errp, "Failed to convert system time %d",
+                       (int)GetLastError());
+            return;
+        }
+    } else {
+        /* Otherwise read the time from RTC which contains the correct value.
+         * Hopefully. */
+        GetSystemTime(&ts);
+        if (ts.wYear < 1601 || ts.wYear > 30827) {
+            error_setg(errp, "Failed to get time");
+            return;
+        }
     }
 
     acquire_privilege(SE_SYSTEMTIME_NAME, errp);
diff --git a/qga/qapi-schema.json b/qga/qapi-schema.json
index 245f968..80edca1 100644
--- a/qga/qapi-schema.json
+++ b/qga/qapi-schema.json
@@ -120,17 +120,18 @@
 # This command tries to set guest time to the given value,
 # then sets the Hardware Clock to the current System Time.
 # This will make it easier for a guest to resynchronize
-# without waiting for NTP.
+# without waiting for NTP. If no @time is specified, then
+# the time to set is read from RTC.
 #
-# @time: time of nanoseconds, relative to the Epoch of
-#        1970-01-01 in UTC.
+# @time: #optional time of nanoseconds, relative to the Epoch
+#        of 1970-01-01 in UTC.
 #
 # Returns: Nothing on success.
 #
 # Since: 1.5
 ##
 { 'command': 'guest-set-time',
-  'data': { 'time': 'int' } }
+  'data': { '*time': 'int' } }
 
 ##
 # @GuestAgentCommandInfo: