diff --git a/formtools/utils.py b/formtools/utils.py
index 033541f..55aadda 100644
--- a/formtools/utils.py
+++ b/formtools/utils.py
@@ -1,9 +1,30 @@
 import pickle
 
 from django.core.files.uploadedfile import TemporaryUploadedFile
+from django.db.models import QuerySet
 from django.utils.crypto import salted_hmac
 
 
+def sanitise(obj):
+    if isinstance(obj, list):
+        return [sanitise(o) for o in obj]
+    elif isinstance(obj, tuple):
+        return tuple([sanitise(o) for o in obj])
+    elif isinstance(obj, QuerySet):
+        return [sanitise(o) for o in list(obj)]
+    try:
+        od = obj.__dict__
+        nd = {'_class': obj.__class__}
+        for key, val in od.items():
+            if not key.startswith('_'):
+                # ignore Django internal attributes
+                nd[key] = sanitise(val)
+        return nd
+    except Exception:
+        pass
+    return obj
+
+
 def form_hmac(form):
     """
     Calculates a security hash for the given Form instance.
@@ -22,6 +43,7 @@ def form_hmac(form):
             value = value.read()
         data.append((bf.name, value))
 
-    pickled = pickle.dumps(data, pickle.HIGHEST_PROTOCOL)
+    sanitised_data = sanitise(data)
+    pickled = pickle.dumps(sanitised_data, pickle.HIGHEST_PROTOCOL)
     key_salt = 'django.contrib.formtools'
     return salted_hmac(key_salt, pickled).hexdigest()
diff --git a/tests/forms.py b/tests/forms.py
index 85534f5..714723d 100644
--- a/tests/forms.py
+++ b/tests/forms.py
@@ -1,4 +1,32 @@
 from django import forms
+from django.db import models
+
+
+class ManyModel(models.Model):
+    name = models.CharField(max_length=100)
+
+    class Meta:
+        app_label = 'formtools'
+
+    def __str__(self):
+        return self.name
+
+
+class OtherModel(models.Model):
+    name = models.CharField(max_length=100)
+    manymodels = models.ManyToManyField(ManyModel)
+
+    class Meta:
+        app_label = 'formtools'
+
+    def __str__(self):
+        return self.name + " with " + ", ".join(map(str, self.manymodels.all()))
+
+
+class OtherModelForm(forms.ModelForm):
+    class Meta:
+        model = OtherModel
+        fields = ["name", "manymodels"]
 
 
 class TestForm(forms.Form):
diff --git a/tests/tests.py b/tests/tests.py
index f9a2a35..7c8f37d 100644
--- a/tests/tests.py
+++ b/tests/tests.py
@@ -13,7 +13,8 @@
 from formtools import preview, utils
 
 from .forms import (
-    HashTestBlankForm, HashTestForm, HashTestFormWithFile, TestForm,
+    HashTestBlankForm, HashTestForm, HashTestFormWithFile, ManyModel,
+    OtherModelForm, TestForm,
 )
 
 success_string = "Done was called!"
@@ -214,3 +215,28 @@ def test_hash_with_file(self):
             hash1 = utils.form_hmac(f1)
             hash2 = utils.form_hmac(f2)
         self.assertNotEqual(hash1, hash2)
+
+
+class PicklingTests(unittest.TestCase):
+
+    def setUp(self):
+        super().setUp()
+        ManyModel.objects.create(name="jane")
+
+    def test_queryset_hash(self):
+        """
+        Regression test for #10034: the hash generation function should ignore
+        leading/trailing whitespace so as to be friendly to broken browsers that
+        submit it (usually in textareas).
+        """
+
+        qs1 = ManyModel.objects.all()
+        qs2 = ManyModel.objects.all()
+
+        qs1._prefetch_done = True
+        qs2._prefetch_done = False
+        f1 = OtherModelForm({'name': 'joe', 'manymodels': qs1})
+        f2 = OtherModelForm({'name': 'joe', 'manymodels': qs2})
+        hash1 = utils.form_hmac(f1)
+        hash2 = utils.form_hmac(f2)
+        self.assertEqual(hash1, hash2)