diff --git a/x-pack/plugins/fleet/common/services/validate_package_policy.test.ts b/x-pack/plugins/fleet/common/services/validate_package_policy.test.ts
index 98056d6906c59..afb6a2f806f9a 100644
--- a/x-pack/plugins/fleet/common/services/validate_package_policy.test.ts
+++ b/x-pack/plugins/fleet/common/services/validate_package_policy.test.ts
@@ -606,6 +606,132 @@ describe('Fleet - validatePackagePolicy()', () => {
         },
       });
     });
+
+    it('returns package policy validation error if input var does not exist', () => {
+      expect(
+        validatePackagePolicy(
+          {
+            description: 'Linux Metrics',
+            enabled: true,
+            inputs: [
+              {
+                enabled: true,
+                streams: [
+                  {
+                    data_stream: {
+                      dataset: 'linux.memory',
+                      type: 'metrics',
+                    },
+                    enabled: true,
+                  },
+                ],
+                type: 'linux/metrics',
+                vars: {
+                  period: {
+                    type: 'string',
+                    value: '1s',
+                  },
+                },
+              },
+            ],
+            name: 'linux-3d13ada6-a9ae-46df-8e57-ff5050f4b671',
+            namespace: 'default',
+            output_id: '',
+            package: {
+              name: 'linux',
+              title: 'Linux Metrics',
+              version: '0.6.2',
+            },
+            policy_id: 'b25cb6e0-8347-11ec-96f9-6590c25bacf9',
+          },
+          {
+            ...mockPackage,
+            name: 'linux',
+            policy_templates: [
+              {
+                name: 'system',
+                title: 'Linux kernel metrics',
+                description: 'Collect system metrics from Linux operating systems',
+                inputs: [
+                  {
+                    title: 'Collect system metrics from Linux instances',
+                    vars: [
+                      {
+                        name: 'system.hostfs',
+                        type: 'text',
+                        title: 'Proc Filesystem Directory',
+                        multi: false,
+                        required: false,
+                        show_user: true,
+                        description: 'The proc filesystem base directory.',
+                      },
+                    ],
+                    type: 'system/metrics',
+                    description:
+                      'Collecting Linux entropy, Network Summary, RAID, service, socket, and users metrics',
+                  },
+                  {
+                    title: 'Collect low-level system metrics from Linux instances',
+                    vars: [],
+                    type: 'linux/metrics',
+                    description: 'Collecting Linux conntrack, ksm, pageinfo metrics.',
+                  },
+                ],
+                multiple: true,
+              },
+            ],
+            data_streams: [
+              {
+                dataset: 'linux.memory',
+                package: 'linux',
+                path: 'memory',
+                streams: [
+                  {
+                    input: 'linux/metrics',
+                    title: 'Linux memory metrics',
+                    vars: [
+                      {
+                        name: 'period',
+                        type: 'text',
+                        title: 'Period',
+                        multi: false,
+                        required: true,
+                        show_user: true,
+                        default: '10s',
+                      },
+                    ],
+                    template_path: 'stream.yml.hbs',
+                    description: 'Linux paging and memory management metrics',
+                  },
+                ],
+                title: 'Linux-only memory metrics',
+                release: 'experimental',
+                type: 'metrics',
+              },
+            ],
+          },
+          safeLoad
+        )
+      ).toEqual({
+        description: null,
+        inputs: {
+          'linux/metrics': {
+            streams: {
+              'linux.memory': {
+                vars: {
+                  period: ['Period is required'],
+                },
+              },
+            },
+            vars: {
+              period: ['period var definition does not exist'],
+            },
+          },
+        },
+        name: null,
+        namespace: null,
+      });
+    });
   });
 
   describe('works for packages with multiple policy templates (aka integrations)', () => {
diff --git a/x-pack/plugins/fleet/common/services/validate_package_policy.ts b/x-pack/plugins/fleet/common/services/validate_package_policy.ts
index b6befdf8c790e..f1e28bfbe4e55 100644
--- a/x-pack/plugins/fleet/common/services/validate_package_policy.ts
+++ b/x-pack/plugins/fleet/common/services/validate_package_policy.ts
@@ -143,7 +143,7 @@ export const validatePackagePolicy = (
         results[name] = input.enabled
           ? validatePackagePolicyConfig(
               configEntry,
-              inputVarDefsByPolicyTemplateAndType[inputKey][name],
+              (inputVarDefsByPolicyTemplateAndType[inputKey] ?? {})[name],
               name,
               safeLoadYaml
             )
@@ -210,10 +210,15 @@ export const validatePackagePolicyConfig = (
   }
 
   if (varDef === undefined) {
-    // eslint-disable-next-line no-console
-    console.debug(`No variable definition for ${varName} found`);
-
-    return null;
+    errors.push(
+      i18n.translate('xpack.fleet.packagePolicyValidation.nonExistentVarMessage', {
+        defaultMessage: '{varName} var definition does not exist',
+        values: {
+          varName,
+        },
+      })
+    );
+    return errors;
   }
 
   if (varDef.required) {