diff --git a/nova/api/openstack/placement/requestlog.py b/nova/api/openstack/placement/requestlog.py
index ad071d78f..8b3639e76 100644
--- a/nova/api/openstack/placement/requestlog.py
+++ b/nova/api/openstack/placement/requestlog.py
@@ -36,6 +36,10 @@ class RequestLog(object):
         LOG.debug('Starting request: %s "%s %s"',
                   environ['REMOTE_ADDR'], environ['REQUEST_METHOD'],
                    self._get_uri(environ))
+        # Set the accept header if it is not otherwise set. This
+        # ensures that error responses will be in JSON.
+        if not environ.get('HTTP_ACCEPT'):
+            environ['HTTP_ACCEPT'] = 'application/json'
         if LOG.isEnabledFor(logging.INFO):
             return self._log_app(environ, start_response)
         else:
diff --git a/nova/tests/functional/api/openstack/placement/gabbits/bug-1674694.yaml b/nova/tests/functional/api/openstack/placement/gabbits/bug-1674694.yaml
new file mode 100644
index 000000000..609f01574
--- /dev/null
+++ b/nova/tests/functional/api/openstack/placement/gabbits/bug-1674694.yaml
@@ -0,0 +1,38 @@
+# Test launchpad bug https://bugs.launchpad.net/nova/+bug/1674694
+
+fixtures:
+    - APIFixture
+
+defaults:
+    request_headers:
+        x-auth-token: admin
+
+tests:
+
+- name: 404 with application/json
+  GET: /bc8d9d50-7b0d-45ef-839c-e7b5e1c4e8fd
+  request_headers:
+      accept: application/json
+  status: 404
+  response_headers:
+      content-type: application/json
+  response_json_paths:
+      $.errors[0].status: 404
+
+- name: 404 with no accept
+  GET: /bc8d9d50-7b0d-45ef-839c-e7b5e1c4e8fd
+  status: 404
+  response_headers:
+      content-type: application/json
+  response_json_paths:
+      $.errors[0].status: 404
+
+- name: 404 with other accept
+  GET: /bc8d9d50-7b0d-45ef-839c-e7b5e1c4e8fd
+  status: 404
+  request_headers:
+      accept: text/html
+  response_headers:
+      content-type: /text/html/
+  response_strings:
+      - The resource could not be found
diff --git a/nova/tests/functional/api/openstack/placement/gabbits/microversion-bug-1724065.yaml b/nova/tests/functional/api/openstack/placement/gabbits/microversion-bug-1724065.yaml
new file mode 100644
index 000000000..718faaf02
--- /dev/null
+++ b/nova/tests/functional/api/openstack/placement/gabbits/microversion-bug-1724065.yaml
@@ -0,0 +1,22 @@
+# Test launchpad bug https://bugs.launchpad.net/nova/+bug/1724065
+
+fixtures:
+    - APIFixture
+
+defaults:
+    request_headers:
+        x-auth-token: user
+
+tests:
+
+# min version from start of placement time is 1.0
+# Without the fix, this results in a 500 with an 'HTTP_ACCEPT'
+# KeyError.
+- name: no accept header and out of range microversion
+  GET: /resource_providers
+  request_headers:
+      openstack-api-version: placement 0.9
+  status: 406
+  response_strings:
+      - Unacceptable version header
+
diff --git a/nova/tests/functional/api/openstack/placement/gabbits/traits.yaml b/nova/tests/functional/api/openstack/placement/gabbits/traits.yaml
index c8e6ba9bb..6cdadf138 100644
--- a/nova/tests/functional/api/openstack/placement/gabbits/traits.yaml
+++ b/nova/tests/functional/api/openstack/placement/gabbits/traits.yaml
@@ -13,13 +13,13 @@ tests:
   PUT: /traits/TRAIT_X
   status: 400
   response_strings:
-    - 'The trait is invalid. A valid trait must include prefix "CUSTOM_" and use following characters: "A"-"Z", "0"-"9" and "_"'
+    - 'The trait is invalid. A valid trait must include prefix \"CUSTOM_\" and use following characters: \"A\"-\"Z\", \"0\"-\"9\" and \"_\"'
 
 - name: create a trait with invalid characters
   PUT: /traits/CUSTOM_ABC:1
   status: 400
   response_strings:
-    - 'The trait is invalid. A valid trait must include prefix "CUSTOM_" and use following characters: "A"-"Z", "0"-"9" and "_"'
+    - 'The trait is invalid. A valid trait must include prefix \"CUSTOM_\" and use following characters: \"A\"-\"Z\", \"0\"-\"9\" and \"_\"'
 
 - name: create a trait
   PUT: /traits/CUSTOM_TRAIT_1
@@ -93,7 +93,7 @@ tests:
   GET: /traits?name=in_abc
   status: 400
   response_strings:
-    - 'Badly formatted name parameter. Expected name query string parameter in form: ?name=[in|startswith]:[name1,name2|prefix]. Got: "in_abc"'
+    - 'Badly formatted name parameter. Expected name query string parameter in form: ?name=[in|startswith]:[name1,name2|prefix]. Got: \"in_abc\"'
 
 - name: list traits with name=in filter
   GET: /traits?name=in:CUSTOM_TRAIT_1,CUSTOM_TRAIT_2
@@ -177,7 +177,7 @@ tests:
   GET: /traits?associated=xyz
   status: 400
   response_strings:
-    - 'The query parameter "associated" only accepts "true" or "false"'
+    - 'The query parameter \"associated\" only accepts \"true\" or \"false\"'
 
 - name: set traits for resource provider without resource provider generation
   PUT: /resource_providers/$ENVIRON['RP_UUID']/traits