diff --git a/pymzml/spec.py b/pymzml/spec.py
index db9bc7c..3001e8f 100755
--- a/pymzml/spec.py
+++ b/pymzml/spec.py
@@ -904,8 +904,9 @@ def scan_time(self):
             scan_time_ele = self.element.find(
                 ".//*[@accession='MS:1000016']".format(ns=self.ns)
             )
-            self._scan_time = float(scan_time_ele.attrib.get("value"))
-            self._scan_time_unit = scan_time_ele.get("unitName", "unicorns")
+            if scan_time_ele is not None:
+                self._scan_time = float(scan_time_ele.attrib.get("value"))
+                self._scan_time_unit = scan_time_ele.get("unitName", "unicorns")
         return self._scan_time, self._scan_time_unit
 
     # @property