diff --git a/securedrop_export/export.py b/securedrop_export/export.py
index 7e20728..8dcff76 100755
--- a/securedrop_export/export.py
+++ b/securedrop_export/export.py
@@ -80,7 +80,9 @@ def __init__(self, archive, config_path):
         try:
             with open(config_path) as f:
                 json_config = json.loads(f.read())
-                self.pci_bus_id = int(json_config.get("pci_bus_id", 2))
+                self.pci_bus_id = json_config.get("pci_bus_id", None)
+                if self.pci_bus_id is None:
+                  raise
         except Exception:
             self.exit_gracefully("ERROR_CONFIG")
 
@@ -132,12 +134,15 @@ def extract_tarball(self):
             self.exit_gracefully(msg)
 
     def check_usb_connected(self):
-        p = subprocess.check_output(["lsusb", "-s", self.pci_bus_id])
-        # Empty string means a likely wrong pci_bus_id
-        if p == "":
-            msg = "ERROR_USB_CHECK"
+
+        # If the USB is not attached via qvm-usb attach, lsusb will return empty string and a
+        # return code of 1
+        try:
+          p = subprocess.check_output(["lsusb", "-s", "{}:".format(self.pci_bus_id)])
+        except subprocess.CalledProcessError:
+            msg = "ERROR_USB_CONFIGURATION"
             self.exit_gracefully(msg)
-        n_usb = len(p.rstrip().split("\n"))
+        n_usb = len(p.decode("utf-8").rstrip().split("\n"))
         # If there is one device, it is the root hub.
         if n_usb == 1:
             msg = "USB_NOT_CONNECTED"
diff --git a/tests/sd-export-config-bad-2.json b/tests/sd-export-config-bad-2.json
index 879fb83..f69e25b 100644
--- a/tests/sd-export-config-bad-2.json
+++ b/tests/sd-export-config-bad-2.json
@@ -1,3 +1,3 @@
 {
-  "pci_bus_id": "two"
+  "no_pci_bus_id": "nope"
 }
diff --git a/tests/test_export.py b/tests/test_export.py
index 19be561..d0a2946 100644
--- a/tests/test_export.py
+++ b/tests/test_export.py
@@ -2,6 +2,7 @@
 
 import os
 import pytest
+import subprocess
 import tempfile
 
 from securedrop_export import export
@@ -9,10 +10,10 @@
 SAMPLE_OUTPUT_NO_PRINTER = b"network beh\nnetwork https\nnetwork ipp\nnetwork ipps\nnetwork http\nnetwork\nnetwork ipp14\nnetwork lpd"  # noqa
 SAMPLE_OUTPUT_BOTHER_PRINTER = b"network beh\nnetwork https\nnetwork ipp\nnetwork ipps\nnetwork http\nnetwork\nnetwork ipp14\ndirect usb://Brother/HL-L2320D%20series?serial=A00000A000000\nnetwork lpd"  # noqa
 
-SAMPLE_OUTPUT_NO_USB = "Bus 001 Device 001: ID 1d6b:0002 Linux Foundation 2.0 root hub"  # noqa
-SAMPLE_OUTPUT_USB = "Bus 001 Device 002: ID 0781:5575 SanDisk Corp.\nBus 001 Device 001: ID 1d6b:0002 Linux Foundation 2.0 root hub"  # noqa
-SAMPLE_OUTPUT_USB_ERROR = ""
-SAMPLE_OUTPUT_USB_ERROR2 = "h\ne\nl\nl\no"
+SAMPLE_OUTPUT_NO_USB = b"Bus 001 Device 001: ID 1d6b:0002 Linux Foundation 2.0 root hub"  # noqa
+SAMPLE_OUTPUT_USB = b"Bus 001 Device 002: ID 0781:5575 SanDisk Corp.\nBus 001 Device 001: ID 1d6b:0002 Linux Foundation 2.0 root hub"  # noqa
+SAMPLE_OUTPUT_USB_ERROR = b""
+SAMPLE_OUTPUT_USB_ERROR2 = b"h\ne\nl\nl\no"
 TEST_CONFIG = os.path.join(os.path.dirname(__file__), "sd-export-config.json")
 BAD_TEST_CONFIG = os.path.join(os.path.dirname(__file__), "sd-export-config-bad.json")
 ANOTHER_BAD_TEST_CONFIG = os.path.join(os.path.dirname(__file__), "sd-export-config-bad-2.json")
@@ -46,7 +47,7 @@ def test_bad_sd_export_config_invalid_value(capsys):
 
 def test_good_sd_export_config(capsys):
     submission = export.SDExport("", TEST_CONFIG)
-    assert submission.pci_bus_id == 2
+    assert submission.pci_bus_id == "2"
 
 
 def test_exit_gracefully_no_exception(capsys):
@@ -230,7 +231,7 @@ def test_usb_precheck_disconnected(mocked_call, capsys):
     assert captured.err == "{}\n".format(expected_message)
 
 
-@mock.patch("subprocess.check_output", return_value=SAMPLE_OUTPUT_USB_ERROR)
+@mock.patch("subprocess.check_output", return_code=1)
 def test_usb_precheck_error(mocked_call, capsys):
     submission = export.SDExport("testfile", TEST_CONFIG)
     expected_message = "ERROR_USB_CHECK"