diff --git a/nova/exception.py b/nova/exception.py
index 9105d6a51120..0e0af13535d9 100644
--- a/nova/exception.py
+++ b/nova/exception.py
@@ -1956,3 +1956,8 @@ class UnsupportedImageModel(Invalid):
 
 class HostMappingNotFound(Invalid):
     msg_fmt = _("Host '%(name)s' is not mapped to any cell")
+
+
+class RealtimeConfigurationInvalid(Invalid):
+    msg_fmt = _("Cannot set realtime policy in a non dedicated "
+                "cpu pinning policy")
diff --git a/nova/tests/unit/virt/test_hardware.py b/nova/tests/unit/virt/test_hardware.py
index 27d8fe6f2930..fb38601fc2f3 100644
--- a/nova/tests/unit/virt/test_hardware.py
+++ b/nova/tests/unit/virt/test_hardware.py
@@ -1090,6 +1090,18 @@ class NUMATopologyTest(test.NoDBTestCase):
                 },
                 "expect": exception.ImageCPUPinningForbidden,
             },
+            {
+                # Invalid CPU pinning policy with realtime
+                "flavor": objects.Flavor(vcpus=4, memory_mb=2048,
+                                         extra_specs={
+                                             "hw:cpu_policy": "shared",
+                                             "hw:cpu_realtime": "yes",
+                                         }),
+                "image": {
+                    "properties": {}
+                },
+                "expect": exception.RealtimeConfigurationInvalid,
+            },
         ]
 
         for testitem in testdata:
diff --git a/nova/virt/hardware.py b/nova/virt/hardware.py
index 0b87b795ac26..b44dadbab1f6 100644
--- a/nova/virt/hardware.py
+++ b/nova/virt/hardware.py
@@ -958,6 +958,11 @@ def _numa_get_constraints_manual(nodes, flavor, cpu_list, mem_list):
     return objects.InstanceNUMATopology(cells=cells)
 
 
+def is_realtime_enabled(flavor):
+    flavor_rt = flavor.get('extra_specs', {}).get("hw:cpu_realtime")
+    return strutils.bool_from_string(flavor_rt)
+
+
 def _numa_get_constraints_auto(nodes, flavor):
     if ((flavor.vcpus % nodes) > 0 or
         (flavor.memory_mb % nodes) > 0):
@@ -988,6 +993,11 @@ def _add_cpu_pinning_constraint(flavor, image_meta, numa_topology):
     else:
         requested = image_pinning == "dedicated"
 
+    rt = is_realtime_enabled(flavor)
+    pi = image_pinning or flavor_pinning
+    if rt and pi != "dedicated":
+        raise exception.RealtimeConfigurationInvalid()
+
     if not requested:
         return numa_topology