diff --git a/scripts/jenkins.py b/scripts/jenkins.py
index e7ef02916..752bec031 100644
--- a/scripts/jenkins.py
+++ b/scripts/jenkins.py
@@ -273,6 +273,12 @@ class MSVCBuilder(Builder):
 
         os.environ.update(vs_env)
 
+        # On Windows, the default Qt logger doesn't write to stderr, but uses
+        # the Win32 API OutputDebugString instead, which Jenkins can't see.
+        # This environment variable forces it to use stderr. It also forces
+        # QPlainTestLogger::outputMessage to print to stdout.
+        os.environ['QT_FORCE_STDERR_LOGGING'] = '1'
+
     def _get_qmake_spec(self):
         return 'win32-msvc'
 
@@ -294,6 +300,9 @@ class MinGWBuilder(Builder):
         os.environ['PATH'] += os.pathsep + gcc_path
         os.environ['PATH'] += os.pathsep + path.abspath(path.join('c:', os.sep, 'Program Files', '7-Zip'))
 
+        # See comment in MSVCBuilder.
+        os.environ['QT_FORCE_STDERR_LOGGING'] = '1'
+
     def _get_qmake_spec(self):
         return 'win32-g++'