diff --git a/artiq/gui/entries.py b/artiq/gui/entries.py
index 8dc0a9ea3..2eab00ad6 100644
--- a/artiq/gui/entries.py
+++ b/artiq/gui/entries.py
@@ -212,14 +212,15 @@ class _ExplicitScan(LayoutWidget):
         self.addWidget(QtWidgets.QLabel("Sequence:"), 0, 0)
         self.addWidget(self.value, 0, 1)
 
-        float_regexp = "[-+]?[0-9]*\.?[0-9]+([eE][-+]?[0-9]+)?"
+        float_regexp = r"(([+-]?\d+(\.\d*)?|\.\d+)([eE][+-]?\d+)?)"
         regexp = "(float)?( +float)* *".replace("float", float_regexp)
         self.value.setValidator(QtGui.QRegExpValidator(QtCore.QRegExp(regexp),
                                                        self.value))
 
         self.value.setText(" ".join([str(x) for x in state["sequence"]]))
         def update(text):
-            state["sequence"] = [float(x) for x in text.split()]
+            if self.value.hasAcceptableInput():
+                state["sequence"] = [float(x) for x in text.split()]
         self.value.textEdited.connect(update)