diff --git a/fastboot/fastboot.c b/fastboot/fastboot.c
index c81222a..8e92017 100644
--- a/fastboot/fastboot.c
+++ b/fastboot/fastboot.c
@@ -165,6 +165,9 @@
 {
     if (match_fastboot(info) == 0) {
         char* serial = info->serial_number;
+        if (!info->writable) {
+            serial = "no permissions"; // like "adb devices"
+        }
         if (!serial[0]) {
             serial = "????????????";
         }
diff --git a/fastboot/usb.h b/fastboot/usb.h
index f3ec5bf..cc157d5 100644
--- a/fastboot/usb.h
+++ b/fastboot/usb.h
@@ -50,6 +50,8 @@
     unsigned char has_bulk_in;
     unsigned char has_bulk_out;
     
+    unsigned char writable;
+
     char serial_number[256];
 };
   
diff --git a/fastboot/usb_linux.c b/fastboot/usb_linux.c
index 3b40ba7..088c23a 100644
--- a/fastboot/usb_linux.c
+++ b/fastboot/usb_linux.c
@@ -89,7 +89,8 @@
     return 0;
 }
 
-static int filter_usb_device(int fd, char *ptr, int len, ifc_match_func callback,
+static int filter_usb_device(int fd, char *ptr, int len, int writable,
+                             ifc_match_func callback,
                              int *ept_in_id, int *ept_out_id, int *ifc_id)
 {
     struct usb_device_descriptor *dev;
@@ -119,7 +120,8 @@
     info.dev_class = dev->bDeviceClass;
     info.dev_subclass = dev->bDeviceSubClass;
     info.dev_protocol = dev->bDeviceProtocol;
-
+    info.writable = writable;
+    
     // read device serial number (if there is one)
     info.serial_number[0] = 0;
     if (dev->iSerialNumber) {
@@ -201,6 +203,7 @@
     DIR *busdir, *devdir;
     struct dirent *de;
     int fd;
+    int writable = 1;
     
     busdir = opendir(base);
     if(busdir == 0) return 0;
@@ -220,12 +223,18 @@
 
 //            DBG("[ scanning %s ]\n", devname);
             if((fd = open(devname, O_RDWR)) < 0) {
-                continue;
+                // Check if we have read-only access, so we can give a helpful
+                // diagnostic like "adb devices" does.
+                writable = 0;
+                if((fd = open(devname, O_RDONLY)) < 0) {
+                    continue;
+                }
             }
 
             n = read(fd, desc, sizeof(desc));
             
-            if(filter_usb_device(fd, desc, n, callback, &in, &out, &ifc) == 0){
+            if(filter_usb_device(fd, desc, n, writable, callback,
+                                 &in, &out, &ifc) == 0) {
                 usb = calloc(1, sizeof(usb_handle));
                 strcpy(usb->fname, devname);
                 usb->ep_in = in;
@@ -375,5 +384,3 @@
 {
     return find_usb_device("/dev/bus/usb", callback);
 }
-
-
diff --git a/fastboot/usb_osx.c b/fastboot/usb_osx.c
index d6a8260..0b0512d 100644
--- a/fastboot/usb_osx.c
+++ b/fastboot/usb_osx.c
@@ -351,6 +351,7 @@
         // device has no serial number
         handle->info.serial_number[0] = 0;
     }
+    handle->info.writable = 1;
 
     if (try_interfaces(dev, handle)) {
         goto error;
@@ -416,8 +417,6 @@
             break;
         }
 
-        usb_ifc_info info;
-
         if (try_device(device, &h) != 0) {
             IOObjectRelease(device);
             ret = -1;
diff --git a/fastboot/usb_windows.c b/fastboot/usb_windows.c
index 9c0a9cb..54008a4 100644
--- a/fastboot/usb_windows.c
+++ b/fastboot/usb_windows.c
@@ -301,6 +301,7 @@
     info.ifc_class = interf_desc.bInterfaceClass;
     info.ifc_subclass = interf_desc.bInterfaceSubClass;
     info.ifc_protocol = interf_desc.bInterfaceProtocol;
+    info.writable = 1;
     
     // read serial number (if there is one)
     unsigned long serial_number_len = sizeof(info.serial_number);