diff --git a/tests/resources/installrdf/doctype.rdf b/tests/resources/installrdf/doctype.rdf
new file mode 100644
index 0000000..d576c6a
--- /dev/null
+++ b/tests/resources/installrdf/doctype.rdf
@@ -0,0 +1,33 @@
+<?xml version="1.0"?>
+<!DOCTYPE overlay SYSTEM "chrome://helloworld/locale/overlay.dtd">
+
+<RDF xmlns="http://www.w3.org/1999/02/22-rdf-syntax-ns#"
+		xmlns:em="http://www.mozilla.org/2004/em-rdf#">
+
+	<Description about="urn:mozilla:install-manifest">
+	
+	<em:type>2</em:type>
+	
+	<em:id>bastatestapp1@basta.mozilla.com</em:id>
+	<em:version>1.2.3.4</em:version>
+	<em:name>name_value</em:name>
+	<em:description>description_value</em:description>
+	<em:creator>creator_value</em:creator>
+	<em:homepageURL>hompage_url_value</em:homepageURL>
+
+	<em:contributor>contributor_1_value</em:contributor>
+	<em:contributor>contributor_2_value</em:contributor>
+	<em:contributor>contributor_3_value</em:contributor>
+	<em:contributor>contributor_4_value</em:contributor>
+	
+	<em:targetApplication>
+		<Description>
+		<em:id>{ec8030f7-c20a-464f-9b0e-13a3a9e97384}</em:id>
+		<em:minVersion>3.7a5pre</em:minVersion>
+		<em:maxVersion>0.3</em:maxVersion>
+		</Description>
+	</em:targetApplication>
+    
+    </Description>
+    
+</RDF>
diff --git a/tests/test_submain_install_rdf.py b/tests/test_submain_install_rdf.py
index 797be98..f433939 100644
--- a/tests/test_submain_install_rdf.py
+++ b/tests/test_submain_install_rdf.py
@@ -67,4 +67,25 @@ def test_load_irdf_expectation():
     submain.typedetection.detect_type = lambda x, y, z: PACKAGE_THEME
     _run_test("install_rdf.xpi", PACKAGE_EXTENSION, True, True)
     submain.typedetection.detect_type = dt
-    
+   
+def test_doctype():
+    "Asserts that install.rdf files with doctypes break validation"
+
+    err = ErrorBundle()
+    xpi = MockXPIManager(
+            {"install.rdf": "tests/resources/installrdf/doctype.rdf"})
+    assert isinstance(submain._load_install_rdf(err, xpi, None), ErrorBundle)
+    assert err.failed()
+    assert not err.get_resource("has_install_rdf")
+    assert not err.get_resource("install_rdf")
+
+class MockXPIManager(object):
+    "Pretends to be a simple XPI manager"
+
+    def __init__(self, data):
+        self.data = data
+
+    def read(self, name):
+        "Simulates a read operation"
+        assert name in self.data
+        return open(self.data[name]).read()
diff --git a/validator/submain.py b/validator/submain.py
index a11837d..292a4f8 100644
--- a/validator/submain.py
+++ b/validator/submain.py
@@ -1,4 +1,5 @@
 import os
+import re
 
 import zipfile
 
@@ -142,6 +143,18 @@ def test_package(err, file_, name, expectation=PACKAGE_ANY):
 def _load_install_rdf(err, package, expectation):
     # Load up the install.rdf file.
     install_rdf_data = package.read("install.rdf")
+
+    if re.search('<!doctype', install_rdf_data, re.I):
+        err.save_resource("bad_install_rdf", True)
+        return err.error(("main",
+                          "test_package",
+                          "doctype_in_installrdf"),
+                         "DOCTYPEs are not permitted in install.rdf",
+                         "The add-on's install.rdf file contains a DOCTYPE. "
+                         "It must be removed before your add-on can be "
+                         "validated.",
+                         filename="install.rdf")
+
     install_rdf = RDFParser(install_rdf_data)
     
     if install_rdf.rdf is None or not install_rdf:
@@ -149,7 +162,8 @@ def _load_install_rdf(err, package, expectation):
                           "test_package",
                           "cannot_parse_installrdf"),
                          "Cannot Parse install.rdf",
-                         "The install.rdf file could not be parsed.")
+                         "The install.rdf file could not be parsed.",
+                         filename="install.rdf")
     else:
         err.save_resource("has_install_rdf", True)
         err.save_resource("install_rdf", install_rdf)
diff --git a/validator/testcases/packagelayout.py b/validator/testcases/packagelayout.py
index 15dd777..61df4e4 100644
--- a/validator/testcases/packagelayout.py
+++ b/validator/testcases/packagelayout.py
@@ -97,7 +97,8 @@ def test_layout_all(err, package_contents, xpi_package):
     if xpi_package.subpackage:
         return
     
-    if not err.get_resource("has_install_rdf"):
+    if not err.get_resource("has_install_rdf") and \
+       not err.get_resource("bad_install_rdf"):
         err.error(("testcases_packagelayout",
                   "test_layout_all",
                   "missing_install_rdf"),