diff --git a/electrum/test_runner.py b/electrum/test_runner.py
--- a/electrum/test_runner.py
+++ b/electrum/test_runner.py
@@ -2,6 +2,7 @@
 
 import os.path
 import unittest
+from collections.abc import Iterable
 
 # Use realpath in case this script is called via a symbolic link
 ELECTRUM_DIR = os.path.dirname(os.path.realpath(__file__))
@@ -11,6 +12,13 @@
     ELECTRUM_DIR, pattern="test_*.py"
 ):
     for test_suite in all_test_suite:
+        if not isinstance(test_suite, Iterable):
+            # unittest sometimes runs into errors when trying to detect test files, and
+            # then returns a _FailedTest object that makes addTests fail with
+            # `TypeError: '_FailedTest' object is not iterable`
+            # This happens for instance with electrumabc_gui when PyQt5 is missing.
+            # We don't want PyQt5 to be a hard dependency for tests for now:.
+            continue
         suite.addTests(test_suite)
 
 unittest.main(defaultTest="suite")