diff --git a/django/contrib/formtools/tests/__init__.py b/django/contrib/formtools/tests/__init__.py
index b88f565d6b6..1ec71d3e338 100644
--- a/django/contrib/formtools/tests/__init__.py
+++ b/django/contrib/formtools/tests/__init__.py
@@ -233,6 +233,8 @@ class WizardPageOneForm(forms.Form):
 class WizardPageTwoForm(forms.Form):
     field = forms.CharField()
 
+class WizardPageTwoAlternativeForm(forms.Form):
+    field = forms.CharField()
 
 class WizardPageThreeForm(forms.Form):
     field = forms.CharField()
@@ -351,7 +353,8 @@ class WizardTests(TestCase):
 
     def test_14498(self):
         """
-        Regression test for ticket #14498.
+        Regression test for ticket #14498.  All previous steps' forms should be
+        validated.
         """
         that = self
 
@@ -391,3 +394,26 @@ class WizardTests(TestCase):
                 "wizard_step": "1"}
         wizard(DummyRequest(POST=data))
         self.assertTrue(reached[0])
+
+    def test_15075(self):
+        """
+        Regression test for ticket #15075.  Allow modifying wizard's form_list
+        in process_step.
+        """
+        that = self
+
+        class WizardWithProcessStep(WizardClass):
+            def process_step(self, request, form, step):
+                if step == 0:
+                    self.form_list[1] = WizardPageTwoAlternativeForm
+                if step == 1:
+                    that.assertTrue(isinstance(form, WizardPageTwoAlternativeForm))
+
+        wizard = WizardWithProcessStep([WizardPageOneForm,
+                                        WizardPageTwoForm,
+                                        WizardPageThreeForm])
+        data = {"0-field": "test",
+                "1-field": "test2",
+                "hash_0": "7e9cea465f6a10a6fb47fcea65cb9a76350c9a5c",
+                "wizard_step": "1"}
+        wizard(DummyRequest(POST=data))
diff --git a/django/contrib/formtools/wizard.py b/django/contrib/formtools/wizard.py
index e0f5e2c64a6..6f3660dd996 100644
--- a/django/contrib/formtools/wizard.py
+++ b/django/contrib/formtools/wizard.py
@@ -90,6 +90,40 @@ class FormWizard(object):
         if current_step >= self.num_steps():
             raise Http404('Step %s does not exist' % current_step)
 
+        # Validate and process all the previous forms before instantiating the
+        # current step's form in case self.process_step makes changes to
+        # self.form_list.
+
+        # If any of them fails validation, that must mean the validator relied
+        # on some other input, such as an external Web site.
+
+        # It is also possible that alidation might fail under certain attack
+        # situations: an attacker might be able to bypass previous stages, and
+        # generate correct security hashes for all the skipped stages by virtue
+        # of:
+        #  1) having filled out an identical form which doesn't have the
+        #     validation (and does something different at the end),
+        #  2) or having filled out a previous version of the same form which
+        #     had some validation missing,
+        #  3) or previously having filled out the form when they had more
+        #     privileges than they do now.
+        #
+        # Since the hashes only take into account values, and not other other
+        # validation the form might do, we must re-do validation now for
+        # security reasons.
+        previous_form_list = []
+        for i in range(current_step):
+            f = self.get_form(i, request.POST)
+            if not self._check_security_hash(request.POST.get("hash_%d" % i, ''),
+                                             request, f):
+                return self.render_hash_failure(request, i)
+
+            if not f.is_valid():
+                return self.render_revalidation_failure(request, i, f)
+            else:
+                self.process_step(request, f, i)
+                previous_form_list.append(f)
+
         # Process the current step. If it's valid, go to the next step or call
         # done(), depending on whether any steps remain.
         if request.method == 'POST':
@@ -98,36 +132,6 @@ class FormWizard(object):
             form = self.get_form(current_step)
 
         if form.is_valid():
-            # Validate all the forms. If any of them fail validation, that
-            # must mean the validator relied on some other input, such as
-            # an external Web site.
-
-            # It is also possible that validation might fail under certain
-            # attack situations: an attacker might be able to bypass previous
-            # stages, and generate correct security hashes for all the
-            # skipped stages by virtue of:
-            #  1) having filled out an identical form which doesn't have the
-            #     validation (and does something different at the end),
-            #  2) or having filled out a previous version of the same form
-            #     which had some validation missing,
-            #  3) or previously having filled out the form when they had
-            #     more privileges than they do now.
-            #
-            # Since the hashes only take into account values, and not other
-            # other validation the form might do, we must re-do validation
-            # now for security reasons.
-            previous_form_list = [self.get_form(i, request.POST) for i in range(current_step)]
-
-            for i, f in enumerate(previous_form_list):
-                if not self._check_security_hash(request.POST.get("hash_%d" % i, ''), request, f):
-                    return self.render_hash_failure(request, i)
-
-                if not f.is_valid():
-                    return self.render_revalidation_failure(request, i, f)
-                else:
-                    self.process_step(request, f, i)
-
-            # Now progress to processing this step:
             self.process_step(request, form, current_step)
             next_step = current_step + 1