diff --git a/nova/tests/functional/libvirt/test_numa_servers.py b/nova/tests/functional/libvirt/test_numa_servers.py
index ae57478cb6dd..31a68ae42272 100644
--- a/nova/tests/functional/libvirt/test_numa_servers.py
+++ b/nova/tests/functional/libvirt/test_numa_servers.py
@@ -323,11 +323,8 @@ class NUMAServersTest(NUMAServersTestBase):
         }
         flavor_id = self._create_flavor(vcpu=4, extra_spec=extra_spec)
 
-        # FIXME(stephenfin): This is bug #1898272. In real life, this
-        # configuration will result in a libvirt traceback due to attempting to
-        # pin the single shared instance vCPU to an empty set
-        # self._run_build_test(flavor_id, end_status='ERROR')
-        self._run_build_test(flavor_id)
+        # There shouldn't be any hosts available to satisfy this request
+        self._run_build_test(flavor_id, end_status='ERROR')
 
     def test_create_server_with_dedicated_policy_old_configuration(self):
         """Create a server using the legacy extra spec and configuration.
diff --git a/nova/tests/unit/virt/test_hardware.py b/nova/tests/unit/virt/test_hardware.py
index c9eff4d81c79..f1b47548cdc5 100644
--- a/nova/tests/unit/virt/test_hardware.py
+++ b/nova/tests/unit/virt/test_hardware.py
@@ -3926,6 +3926,29 @@ class CPUPinningCellTestCase(test.NoDBTestCase, _CPUPinningTestCaseBase):
             mock_log.warning.call_args[0][0],
         )
 
+    def test_get_pinning_mixed_policy_bug_1898272(self):
+        """A host cell must have sufficient dedicated *and* shared CPUs when
+        using the mixed policy.
+        """
+        host_pin = objects.NUMACell(
+            id=0,
+            cpuset=set(),
+            pcpuset=set(range(4)),
+            memory=4096,
+            memory_usage=0,
+            pinned_cpus=set(),
+            siblings=[{0, 2}, {1, 3}],
+            mempages=[],
+        )
+        inst_pin = objects.InstanceNUMACell(
+            cpuset={0},
+            pcpuset={1, 2, 3},
+            memory=2048,
+            cpu_policy=fields.CPUAllocationPolicy.MIXED,
+        )
+        inst_topo = hw._numa_fit_instance_cell(host_pin, inst_pin)
+        self.assertIsNone(inst_topo)
+
 
 class CPUPinningTestCase(test.NoDBTestCase, _CPUPinningTestCaseBase):
     def test_host_numa_fit_instance_to_host_single_cell(self):
diff --git a/nova/virt/hardware.py b/nova/virt/hardware.py
index be64162959bd..1163222f653a 100644
--- a/nova/virt/hardware.py
+++ b/nova/virt/hardware.py
@@ -1121,7 +1121,12 @@ def _numa_fit_instance_cell(
                           'cpuset_reserved': cpuset_reserved
                       })
             return None
-    else:
+
+    if instance_cell.cpu_policy in (
+        fields.CPUAllocationPolicy.SHARED,
+        fields.CPUAllocationPolicy.MIXED,
+        None,
+    ):
         required_cpus = len(instance_cell.cpuset)
         if required_cpus > len(host_cell.cpuset):
             LOG.debug('Not enough host cell CPUs to fit instance cell; '
@@ -1135,7 +1140,7 @@ def _numa_fit_instance_cell(
         fields.CPUAllocationPolicy.DEDICATED,
         fields.CPUAllocationPolicy.MIXED,
     ):
-        LOG.debug('Pinning has been requested')
+        LOG.debug('Instance has requested pinned CPUs')
         required_cpus = len(instance_cell.pcpuset) + cpuset_reserved
         if required_cpus > host_cell.avail_pcpus:
             LOG.debug('Not enough available CPUs to schedule instance. '
@@ -1166,9 +1171,14 @@ def _numa_fit_instance_cell(
             LOG.debug('Failed to map instance cell CPUs to host cell CPUs')
             return None
 
-    elif limits:
-        LOG.debug('No pinning requested, considering limitations on usable cpu'
-                  ' and memory')
+    if instance_cell.cpu_policy in (
+        fields.CPUAllocationPolicy.SHARED,
+        fields.CPUAllocationPolicy.MIXED,
+        None,
+    ) and limits:
+        LOG.debug(
+            'Instance has requested shared CPUs; considering limitations '
+            'on usable CPU and memory.')
         cpu_usage = host_cell.cpu_usage + len(instance_cell.cpuset)
         cpu_limit = len(host_cell.cpuset) * limits.cpu_allocation_ratio
         if cpu_usage > cpu_limit: