diff --git a/waflib/Tools/qt4.py b/waflib/Tools/qt4.py
index 7a4edfa8..63f901bd 100644
--- a/waflib/Tools/qt4.py
+++ b/waflib/Tools/qt4.py
@@ -161,6 +161,7 @@ class qxx(Task.classes['cxx']):
 			return tsk
 
 	def moc_h_ext(self):
+		ext = []
 		try:
 			ext = Options.options.qt_header_ext.split()
 		except AttributeError:
diff --git a/waflib/Tools/qt5.py b/waflib/Tools/qt5.py
index 7341b532..0a2c76e8 100644
--- a/waflib/Tools/qt5.py
+++ b/waflib/Tools/qt5.py
@@ -202,6 +202,7 @@ class qxx(Task.classes['cxx']):
 			delattr(self, 'cache_sig')
 
 	def moc_h_ext(self):
+		ext = []
 		try:
 			ext = Options.options.qt_header_ext.split()
 		except AttributeError: