diff --git a/siputils.py b/siputils.py
index 17935ba..cf02ac0 100644
--- a/siputils.py
+++ b/siputils.py
@@ -568,7 +568,7 @@ class Makefile:
                     elif mod == "phonon":
                         defines.append("QT_PHONON_LIB")
             elif self._threaded:
-                defines.append("QT_THREAD_SUPPORT")
+                defines.append("TQT_THREAD_SUPPORT")
 
             # Handle library directories.
             libdir_qt = self.optional_list("LIBDIR_QT")