diff --git a/ironic/api/middleware/parsable_error.py b/ironic/api/middleware/parsable_error.py
index 6e742c06925..37e7137a7e6 100644
--- a/ironic/api/middleware/parsable_error.py
+++ b/ironic/api/middleware/parsable_error.py
@@ -64,6 +64,11 @@ class ParsableErrorMiddleware(object):
                 state['headers'] = headers
                 return start_response(status, headers, exc_info)
 
+        # The default for ironic is application/json. However, Pecan will try
+        # to output HTML errors if no Accept header is provided.
+        if 'HTTP_ACCEPT' not in environ or environ['HTTP_ACCEPT'] == '*/*':
+            environ['HTTP_ACCEPT'] = 'application/json'
+
         app_iter = self.app(environ, replacement_start_response)
         if (state['status_code'] // 100) not in (2, 3):
             req = webob.Request(environ)
diff --git a/ironic/tests/unit/api/controllers/v1/test_portgroup.py b/ironic/tests/unit/api/controllers/v1/test_portgroup.py
index 38cd447d55e..cefe8d48124 100644
--- a/ironic/tests/unit/api/controllers/v1/test_portgroup.py
+++ b/ironic/tests/unit/api/controllers/v1/test_portgroup.py
@@ -400,8 +400,7 @@ class TestListPortgroups(test_api_base.BaseApiTest):
                                  expect_errors=True,
                                  headers={api_base.Version.string: '1.23'})
         self.assertEqual(http_client.NOT_FOUND, response.status_int)
-        self.assertIn('The resource could not be found.',
-                      response.json['error_message'])
+        self.assertIn('Not Found', response.json['error_message'])
 
     def test_ports_subresource_portgroup_not_found(self):
         non_existent_uuid = 'eeeeeeee-cccc-aaaa-bbbb-cccccccccccc'
diff --git a/ironic/tests/unit/api/test_root.py b/ironic/tests/unit/api/test_root.py
index 3ca47fae45f..bb70a0c8308 100644
--- a/ironic/tests/unit/api/test_root.py
+++ b/ironic/tests/unit/api/test_root.py
@@ -13,6 +13,8 @@
 #    License for the specific language governing permissions and limitations
 #    under the License.
 
+from six.moves import http_client
+
 from ironic.api.controllers.v1 import versions
 from ironic.tests.unit.api import base
 
@@ -35,6 +37,18 @@ class TestRoot(base.BaseApiTest):
                          version1['min_version'])
         self.assertEqual(versions.max_version_string(), version1['version'])
 
+    def test_no_html_errors(self):
+        response = self.get_json('/foo', expect_errors=True)
+        self.assertEqual(http_client.NOT_FOUND, response.status_int)
+        self.assertIn('Not Found', response.json['error_message'])
+        self.assertNotIn('<html', response.json['error_message'])
+
+    def test_no_html_errors2(self):
+        response = self.delete('/v1', expect_errors=True)
+        self.assertEqual(http_client.METHOD_NOT_ALLOWED, response.status_int)
+        self.assertIn('Not Allowed', response.json['error_message'])
+        self.assertNotIn('<html', response.json['error_message'])
+
 
 class TestV1Root(base.BaseApiTest):
 
diff --git a/releasenotes/notes/html-errors-27579342e7e8183b.yaml b/releasenotes/notes/html-errors-27579342e7e8183b.yaml
new file mode 100644
index 00000000000..42cd99ae9db
--- /dev/null
+++ b/releasenotes/notes/html-errors-27579342e7e8183b.yaml
@@ -0,0 +1,5 @@
+---
+fixes:
+  - |
+    The bare metal API no longer returns HTML as part of the ``error_message``
+    field in error responses when no ``Accept`` header is provided.