diff --git a/contest/models.py b/contest/models.py
index fecaa4e..404772e 100644
--- a/contest/models.py
+++ b/contest/models.py
@@ -4,7 +4,7 @@ import datetime
 
 from django.db import models
 from django.contrib.auth.models import AbstractUser
-from django.core.validators import RegexValidator
+from django.core.validators import RegexValidator, MinValueValidator, MaxValueValidator
 from django.db.models import Q, signals
 
 from .validators import CallUsernameValidator
@@ -146,6 +146,7 @@ class Frequency(models.Model):
         return "Channel %s: %s MHz" % (self.channel, self.qrg)
 
 class QSO(models.Model):
+    MAX_NO_VALUE = 1000000
     reportValidator = RegexValidator("[1-5][1-9]")
 
     class Meta:
@@ -162,8 +163,9 @@ class QSO(models.Model):
     reportTX = models.CharField(max_length=7, default=59, verbose_name='RS-S', validators=[reportValidator])
     reportRX = models.CharField(max_length=7, default=59, verbose_name='RS-R', validators=[reportValidator])
 
-    ownNo = models.IntegerField(verbose_name='No')
-    otherNo = models.IntegerField(verbose_name='No-R', null=True, blank=True)
+    ownNo = models.IntegerField(verbose_name='No', validators=[MinValueValidator(1), MaxValueValidator(MAX_NO_VALUE)])
+    otherNo = models.IntegerField(verbose_name='No-R', null=True, blank=True,
+                                  validators=[MinValueValidator(1), MaxValueValidator(MAX_NO_VALUE)])
 
     refStr = models.CharField(max_length=20, verbose_name="EXC")
     ref = models.ForeignKey(Reference, models.SET_NULL, null=True, blank=True)