diff --git a/Makefile b/Makefile
index 907ba08..465b8e9 100644
--- a/Makefile
+++ b/Makefile
@@ -11,12 +11,12 @@ BINDIR = $(PWD)/.state/env/bin
 	$(BINDIR)/python -m pip install -r requirements/dev.txt
 
 build: .state/env/pyvenv.cfg
-	$(BINDIR)/python _internal/generator.py
+	$(BINDIR)/python -m _internal.generator
 
 test: .state/env/pyvenv.cfg
 	$(BINDIR)/pytest
 	$(eval TMPDIR := $(shell mktemp -d))
-	$(BINDIR)/python _internal/generator.py --output $(TMPDIR)/test.py
+	$(BINDIR)/python -m _internal.generator --output $(TMPDIR)/test.py
 	diff trove_classifiers/__init__.py $(TMPDIR)/test.py
 
 lint: .state/env/pyvenv.cfg
diff --git a/_internal/classifiers.py b/_internal/classifiers.py
index 5687f6b..84ed928 100644
--- a/_internal/classifiers.py
+++ b/_internal/classifiers.py
@@ -1,4 +1,4 @@
-from models import ClassifierRoot, ClassifierNode
+from .models import ClassifierRoot, ClassifierNode
 
 classifiers = ClassifierRoot(
     children=[
diff --git a/_internal/exceptions.py b/_internal/exceptions.py
new file mode 100644
index 0000000..f1d15ef
--- /dev/null
+++ b/_internal/exceptions.py
@@ -0,0 +1,2 @@
+class InvalidClassifier(Exception):
+    pass
diff --git a/_internal/generator.py b/_internal/generator.py
index 910a085..1a904bd 100644
--- a/_internal/generator.py
+++ b/_internal/generator.py
@@ -4,7 +4,7 @@
 
 from jinja2 import Template
 
-from classifiers import classifiers
+from .classifiers import classifiers
 
 parser = argparse.ArgumentParser()
 parser.add_argument(
diff --git a/_internal/models.py b/_internal/models.py
index bafbb18..9d3b8fa 100644
--- a/_internal/models.py
+++ b/_internal/models.py
@@ -1,3 +1,6 @@
+from .exceptions import InvalidClassifier
+
+
 class ClassifierRoot:
     def __init__(self, children):
         self.children = children
@@ -23,10 +26,21 @@ def __init__(
         skip=False,
     ):
         if deprecated_by and not deprecated:
-            raise Exception(
+            raise InvalidClassifier(
                 "Using deprecated_by, but not marking the classifier as deprecated"
             )
 
+        if short_name.lower().startswith("private"):
+            raise InvalidClassifier("Classifiers starting with 'Private' are invalid")
+
+        if short_name.strip().rstrip() != short_name:
+            raise InvalidClassifier(
+                "Classifiers starting or ending with whitespace are invalid"
+            )
+
+        if ":" in short_name:
+            raise InvalidClassifier("Classifiers containing ':' are invalid")
+
         self.short_name = short_name
         self.prefix_list = []
         self.deprecated = deprecated
diff --git a/setup.py b/setup.py
index 5a6d2fa..deb5a01 100644
--- a/setup.py
+++ b/setup.py
@@ -3,8 +3,6 @@
 
 from setuptools import setup, find_packages
 
-from trove_classifiers import classifiers
-
 here = path.abspath(path.dirname(__file__))
 
 # Get the long description from the README file
diff --git a/tests/test_classifiers.py b/tests/test_classifiers.py
index d2a7ff0..c11cb6b 100644
--- a/tests/test_classifiers.py
+++ b/tests/test_classifiers.py
@@ -1,6 +1,7 @@
 import pytest
 
 from _internal.models import ClassifierRoot, ClassifierNode
+from _internal.exceptions import InvalidClassifier
 
 
 def test_nested_prefixes():
@@ -13,10 +14,10 @@ def test_nested_prefixes():
         ]
     )
 
-    assert root.generate() == [
-        ClassifierNode("Foo"),
-        ClassifierNode("Foo :: Bar"),
-        ClassifierNode("Foo :: Bar :: Baz"),
+    assert [node.full_name for node in root.generate()] == [
+        "Foo",
+        "Foo :: Bar",
+        "Foo :: Bar :: Baz",
     ]
 
 
@@ -31,12 +32,47 @@ def test_skip():
         ]
     )
 
-    assert root.generate() == [
-        ClassifierNode("Foo :: Bar"),
-        ClassifierNode("Foo :: Bar :: Baz"),
+    assert [node.full_name for node in root.generate()] == [
+        "Foo :: Bar",
+        "Foo :: Bar :: Baz",
     ]
 
 
 def test_bad_deprecation_failure():
-    with pytest.raises(Exception):
+    with pytest.raises(InvalidClassifier) as excinfo:
         ClassifierNode("blah", deprecated_by=["spam"])
+
+    assert excinfo.value.args == (
+        "Using deprecated_by, but not marking the classifier as deprecated",
+    )
+
+
+@pytest.mark.parametrize(
+    "parent, child",
+    [("Private", "Foo"), ("private", "Foo"), ("Foo", "Private"), ("Foo", "private"),],
+)
+def test_private_classifier_failure(parent, child):
+    with pytest.raises(InvalidClassifier) as excinfo:
+        ClassifierNode(
+            parent, children=[ClassifierNode(child)],
+        )
+
+    assert excinfo.value.args == ("Classifiers starting with 'Private' are invalid",)
+
+
+@pytest.mark.parametrize("classifier", [" Foo", "Foo "])
+def test_whitespace_classifier_failure(classifier):
+    with pytest.raises(InvalidClassifier) as excinfo:
+        ClassifierNode(classifier)
+
+    assert excinfo.value.args == (
+        "Classifiers starting or ending with whitespace are invalid",
+    )
+
+
+@pytest.mark.parametrize("classifier", ["Foo:", "Foo :: Bar"])
+def test_colon_classifier_failure(classifier):
+    with pytest.raises(InvalidClassifier) as excinfo:
+        ClassifierNode(classifier)
+
+    assert excinfo.value.args == ("Classifiers containing ':' are invalid",)