--- a/build/mobile/devicemanagerADB.py
+++ b/build/mobile/devicemanagerADB.py
@@ -28,17 +28,17 @@ class DeviceManagerADB(DeviceManager):
   def Init(self, packageName):
     # Initialization code that may fail: Catch exceptions here to allow
     # successful initialization even if, for example, adb is not installed.
     try:
       self.verifyADB()
       self.verifyRunAs(packageName)
     except:
       self.useRunAs = False
-      self.packageName = None
+      self.packageName = packageName
     try:
       self.verifyZip()
     except:
       self.useZip = False
 
     def verifyRoot():
       # a test to see if we have root privs
       files = self.listFiles("/data/data")
@@ -679,17 +679,23 @@ class DeviceManagerADB(DeviceManager):
     # echoing conditions encountered by Fennec at run time.
     # Check to see if run-as can be used here, by verifying a 
     # file copy via run-as.
     self.useRunAs = False
     devroot = self.getDeviceRoot()
     if (packageName and self.isCpAvailable() and devroot):
       tmpDir = self.getTempDir()
 
-      self.checkCmd(["shell", "run-as", packageName, "mkdir", devroot + "/sanity"])
+      # The problem here is that run-as doesn't cause a non-zero exit code
+      # when failing because of a non-existent or non-debuggable package :(
+      runAsOut = self.runCmd(["shell", "run-as", packageName, "mkdir", devroot + "/sanity"]).communicate()[0]
+      if runAsOut.startswith("run-as:") and ("not debuggable" in runAsOut[0] or
+                                             "is unknown" in runAsOut[0]):
+        raise DMError("run-as failed sanity check")
+
       self.checkCmd(["push", os.path.abspath(sys.argv[0]), tmpDir + "/tmpfile"])
       if self.useDDCopy:
         self.checkCmd(["shell", "run-as", packageName, "dd", "if=" + tmpDir + "/tmpfile", "of=" + devroot + "/sanity/tmpfile"])
       else:
         self.checkCmd(["shell", "run-as", packageName, "cp", tmpDir + "/tmpfile", devroot + "/sanity"])
       if (self.fileExists(devroot + "/sanity/tmpfile")):
         print "will execute commands via run-as " + packageName
         self.packageName = packageName