diff --git a/adb/adb.c b/adb/adb.c
index 7df3f7b..a34dd71 100644
--- a/adb/adb.c
+++ b/adb/adb.c
@@ -895,9 +895,10 @@
         ** AID_GRAPHICS to access the frame buffer
         ** AID_NET_BT and AID_NET_BT_ADMIN to diagnose bluetooth (hcidump)
         ** AID_SDCARD_RW to allow writing to the SD card
+        ** AID_MOUNT to allow unmounting the SD card before rebooting
         */
         gid_t groups[] = { AID_ADB, AID_LOG, AID_INPUT, AID_INET, AID_GRAPHICS,
-                           AID_NET_BT, AID_NET_BT_ADMIN, AID_SDCARD_RW };
+                           AID_NET_BT, AID_NET_BT_ADMIN, AID_SDCARD_RW, AID_MOUNT };
         setgroups(sizeof(groups)/sizeof(groups[0]), groups);
 
         /* then switch user and group to "shell" */
diff --git a/adb/services.c b/adb/services.c
index b5df554..487c7d3 100644
--- a/adb/services.c
+++ b/adb/services.c
@@ -176,9 +176,23 @@
 void reboot_service(int fd, void *arg)
 {
     char buf[100];
-    int ret;
+    int pid, ret;
 
     sync();
+
+    /* Attempt to unmount the SD card first.
+     * No need to bother checking for errors.
+     */
+    pid = fork();
+    if (pid == 0) {
+        /* ask vdc to unmount it */
+        execl("/system/bin/vdc", "/system/bin/vdc", "volume", "unmount",
+                getenv("EXTERNAL_STORAGE"), "force", NULL);
+    } else if (pid > 0) {
+        /* wait until vdc succeeds or fails */
+        waitpid(pid, &ret, 0);
+    }
+
     ret = __reboot(LINUX_REBOOT_MAGIC1, LINUX_REBOOT_MAGIC2,
                     LINUX_REBOOT_CMD_RESTART2, (char *)arg);
     if (ret < 0) {