diff --git a/c3l_membership/forms.py b/c3l_membership/forms.py
--- a/c3l_membership/forms.py
+++ b/c3l_membership/forms.py
@@ -2,10 +2,55 @@ from datetime import date
 
 from flask_babel import lazy_gettext
 from flask_wtf import FlaskForm
-from wtforms import BooleanField, DateField, RadioField, StringField, SubmitField
+from wtforms import (
+    BooleanField,
+    DateField,
+    RadioField,
+    StringField,
+    SubmitField,
+    ValidationError,
+)
 from wtforms.validators import Email, InputRequired, Length, Optional
 
 
+class NotEqualTo:
+    """
+    Compares the values of two fields.
+    :param fieldname:
+        The name of the other field to compare to.
+    :param message:
+        Error message to raise in case of a validation error. Can be
+        interpolated with `%(other_label)s` and `%(other_name)s` to provide a
+        more helpful error.
+    """
+
+    def __init__(self, fieldname, message=None):
+        self.fieldname = fieldname
+        self.message = message
+
+    def __call__(self, form, field):
+        try:
+            other = form[self.fieldname]
+        except KeyError as exc:
+            raise ValidationError(
+                field.gettext("Invalid field name '%s'.") % self.fieldname
+            ) from exc
+        if field.data != other.data:
+            return
+
+        d = {
+            "other_label": hasattr(other, "label")
+            and other.label.text
+            or self.fieldname,
+            "other_name": self.fieldname,
+        }
+        message = self.message
+        if message is None:
+            message = field.gettext("Field must not be equal to %(other_name)s.")
+
+        raise ValidationError(message % d)
+
+
 class MembershipForm(FlaskForm):
 
     username = StringField(
@@ -50,6 +95,15 @@ class MembershipForm(FlaskForm):
         lazy_gettext(
             "I am a student and would like to have the reduced membership fees."
         ),
+        validators=[
+            Optional(),
+            NotEqualTo(
+                "starving",
+                lazy_gettext(
+                    "Student and Starving Hacker are mutually exclusive! Please select only one of them."
+                ),
+            ),
+        ],
     )
 
     starving = BooleanField(