diff --git a/cinder/api/schemas/volume_image_metadata.py b/cinder/api/schemas/volume_image_metadata.py
index 7d810f6693d..7b56caf89f1 100644
--- a/cinder/api/schemas/volume_image_metadata.py
+++ b/cinder/api/schemas/volume_image_metadata.py
@@ -27,7 +27,7 @@ set_image_metadata = {
         'os-set_image_metadata': {
             'type': 'object',
             'properties': {
-                'metadata': parameter_types.extra_specs,
+                'metadata': parameter_types.image_metadata,
             },
             'required': ['metadata'],
             'additionalProperties': False,
diff --git a/cinder/api/validation/parameter_types.py b/cinder/api/validation/parameter_types.py
index 2e098c83ab2..cb8203d548f 100644
--- a/cinder/api/validation/parameter_types.py
+++ b/cinder/api/validation/parameter_types.py
@@ -157,6 +157,15 @@ extra_specs = {
     'additionalProperties': False
 }
 
+image_metadata = {
+    'type': 'object',
+    'patternProperties': {
+        '^[a-zA-Z0-9-_:. /]{1,255}$': {
+            'type': 'string', 'format': 'mysql_text'
+        }
+    },
+    'additionalProperties': False
+}
 
 extra_specs_with_no_spaces_key = {
     'type': 'object',
diff --git a/cinder/api/validation/validators.py b/cinder/api/validation/validators.py
index 7369c1ff583..2d714e6ff0d 100644
--- a/cinder/api/validation/validators.py
+++ b/cinder/api/validation/validators.py
@@ -398,6 +398,14 @@ def _validate_key_size(param_value):
     return True
 
 
+@jsonschema.FormatChecker.cls_checks('mysql_text')
+def _validate_mysql_text(param_value):
+    length = len(param_value.encode('utf8'))
+    if length > 65535:
+        return False
+    return True
+
+
 class FormatChecker(jsonschema.FormatChecker):
     """A FormatChecker can output the message from cause exception
 
diff --git a/cinder/tests/unit/api/contrib/test_volume_image_metadata.py b/cinder/tests/unit/api/contrib/test_volume_image_metadata.py
index 16b77d75efd..7ca96fc2379 100644
--- a/cinder/tests/unit/api/contrib/test_volume_image_metadata.py
+++ b/cinder/tests/unit/api/contrib/test_volume_image_metadata.py
@@ -220,6 +220,44 @@ class VolumeImageMetadataTest(test.TestCase):
         self.assertEqual(fake_image_metadata,
                          jsonutils.loads(res.body)["metadata"])
 
+        # Test for value > 255
+        body = {"os-set_image_metadata": {
+            "metadata": {"key": "v" * 260}}
+        }
+        req = webob.Request.blank('/v3/%s/volumes/%s/action' % (
+            fake.PROJECT_ID, fake.VOLUME_ID))
+        req.method = "POST"
+        req.body = jsonutils.dump_as_bytes(body)
+        req.headers["content-type"] = "application/json"
+        fake_get.return_value = {}
+        res = req.get_response(fakes.wsgi_app(
+            fake_auth_context=self.user_ctxt))
+        self.assertEqual(HTTPStatus.OK, res.status_int)
+
+        # This is a weird one ... take a supplementary unicode
+        # char that requires 4 bytes, which will give us a short
+        # string in terms of character count, but a long string
+        # in terms of bytes, and make this string be exactly
+        # 65535 bytes in length.  This should be OK.
+        char4bytes = "\N{CJK UNIFIED IDEOGRAPH-29D98}"
+        self.assertEqual(1, len(char4bytes))
+        self.assertEqual(4, len(char4bytes.encode('utf-8')))
+        str65535bytes = char4bytes * 16383 + '123'
+        self.assertLess(len(str65535bytes), 65535)
+        self.assertEqual(65535, len(str65535bytes.encode('utf-8')))
+        body = {"os-set_image_metadata": {
+            "metadata": {"key": str65535bytes}}
+        }
+        req = webob.Request.blank('/v3/%s/volumes/%s/action' % (
+            fake.PROJECT_ID, fake.VOLUME_ID))
+        req.method = "POST"
+        req.body = jsonutils.dump_as_bytes(body)
+        req.headers["content-type"] = "application/json"
+        fake_get.return_value = {}
+        res = req.get_response(fakes.wsgi_app(
+            fake_auth_context=self.user_ctxt))
+        self.assertEqual(HTTPStatus.OK, res.status_int)
+
     @mock.patch('cinder.objects.Volume.get_by_id')
     def test_create_image_metadata_policy_not_authorized(self, fake_get):
         rules = {
@@ -323,15 +361,38 @@ class VolumeImageMetadataTest(test.TestCase):
                           self.controller.create, req, fake.VOLUME_ID,
                           body=data)
 
-        # Test for long value
+        # Test for very long value
         data = {"os-set_image_metadata": {
-            "metadata": {"key": "v" * 260}}
+            "metadata": {"key": "v" * 65550}}
         }
         req.body = jsonutils.dump_as_bytes(data)
         self.assertRaises(exception.ValidationError,
                           self.controller.create, req, fake.VOLUME_ID,
                           body=data)
 
+        # Test for very long utf8 value
+        data = {"os-set_image_metadata": {
+            "metadata": {"key": "á" * 32775}}
+        }
+        req.body = jsonutils.dump_as_bytes(data)
+        self.assertRaises(exception.ValidationError,
+                          self.controller.create, req, fake.VOLUME_ID,
+                          body=data)
+
+        # Test a short unicode string that actually exceeds
+        # the allowed byte count
+        char4bytes = "\N{CJK UNIFIED IDEOGRAPH-29D98}"
+        str65536bytes = char4bytes * 16384
+        self.assertEqual(65536, len(str65536bytes.encode('utf-8')))
+        self.assertLess(len(str65536bytes), 65535)
+        body = {"os-set_image_metadata": {
+            "metadata": {"key": str65536bytes}}
+        }
+        req.body = jsonutils.dump_as_bytes(body)
+        self.assertRaises(exception.ValidationError,
+                          self.controller.create, req, fake.VOLUME_ID,
+                          body=data)
+
         # Test for empty key.
         data = {"os-set_image_metadata": {
             "metadata": {"": "value1"}}
diff --git a/releasenotes/notes/image-metadata-size-increase-323812970dc0e513.yaml b/releasenotes/notes/image-metadata-size-increase-323812970dc0e513.yaml
new file mode 100644
index 00000000000..14be1817d08
--- /dev/null
+++ b/releasenotes/notes/image-metadata-size-increase-323812970dc0e513.yaml
@@ -0,0 +1,8 @@
+---
+fixes:
+  - |
+    `Bug #1988942 <https://bugs.launchpad.net/cinder/+bug/1988942>`_: Increased
+    size of volume image metadata values accepted by the Block Storage API.
+    Volume image metadata values were limited to 255 characters but Glance
+    allows up to 65535 bytes. This change does not affect the database
+    tables which already allow up to 65535 bytes for image metadata values.