diff --git a/app_config.py b/app_config.py
index 384c7cd..6bbf9b7 100644
--- a/app_config.py
+++ b/app_config.py
@@ -8,7 +8,8 @@
 import logging
 _log = logging.getLogger(__name__)
 
-from PyQt5.QtCore import QSettings
+from PyQt5.QtCore import QSettings, QRegularExpression
+from PyQt5.QtGui import QRegularExpressionValidator
 from PyQt5.QtWidgets import QApplication, QMainWindow
 import json,re
 import numpy as np
@@ -558,6 +559,14 @@ verbose bits:
 
     self._paramTree=pt=ParameterTree(parent=self)
     pt.setParameters(p, showTop=True)
+
+    # restrict prefix/protein fields to alphanumeric characters and underscores,
+    # since these feed directly into DAQ file/directory naming
+    alnum_underscore=QRegularExpressionValidator(QRegularExpression(r'^[A-Za-z0-9_]*$'))
+    for param in (p.param('data acquisition',AppCfg.DAQ_RUN,'prefix'), p.param('data acquisition',AppCfg.DAQ_SAMPLE,'protein')):
+      for item in param.items:
+        item.widget.setValidator(alnum_underscore)
+
     pt.setWindowTitle('SwissMX parameters')
     #t.resize(600, 800)
     self.setCentralWidget(pt)