diff --git a/x-pack/plugins/transform/public/app/sections/create_transform/components/advanced_runtime_mappings_editor/advanced_runtime_mappings_editor.tsx b/x-pack/plugins/transform/public/app/sections/create_transform/components/advanced_runtime_mappings_editor/advanced_runtime_mappings_editor.tsx
index 087bae97e287e..23c4cfcefe8ef 100644
--- a/x-pack/plugins/transform/public/app/sections/create_transform/components/advanced_runtime_mappings_editor/advanced_runtime_mappings_editor.tsx
+++ b/x-pack/plugins/transform/public/app/sections/create_transform/components/advanced_runtime_mappings_editor/advanced_runtime_mappings_editor.tsx
@@ -13,6 +13,7 @@ import { EuiCodeEditor } from '@elastic/eui';
 import { i18n } from '@kbn/i18n';
 
 import { StepDefineFormHook } from '../step_define';
+import { isRuntimeMappings } from '../step_define/common/types';
 
 export const AdvancedRuntimeMappingsEditor: FC<StepDefineFormHook['runtimeMappingsEditor']> = memo(
   ({
@@ -43,8 +44,8 @@ export const AdvancedRuntimeMappingsEditor: FC<StepDefineFormHook['runtimeMappin
           // Try to parse the string passed on from the editor.
           // If parsing fails, the "Apply"-Button will be disabled
           try {
-            JSON.parse(convertToJson(d));
-            setRuntimeMappingsEditorApplyButtonEnabled(true);
+            const parsedJson = JSON.parse(convertToJson(d));
+            setRuntimeMappingsEditorApplyButtonEnabled(isRuntimeMappings(parsedJson));
           } catch (e) {
             setRuntimeMappingsEditorApplyButtonEnabled(false);
           }
diff --git a/x-pack/plugins/transform/public/app/sections/create_transform/components/step_define/common/get_pivot_dropdown_options.ts b/x-pack/plugins/transform/public/app/sections/create_transform/components/step_define/common/get_pivot_dropdown_options.ts
index c88b604989680..f981c3786de34 100644
--- a/x-pack/plugins/transform/public/app/sections/create_transform/components/step_define/common/get_pivot_dropdown_options.ts
+++ b/x-pack/plugins/transform/public/app/sections/create_transform/components/step_define/common/get_pivot_dropdown_options.ts
@@ -26,7 +26,7 @@ import {
 import { getDefaultAggregationConfig } from './get_default_aggregation_config';
 import { getDefaultGroupByConfig } from './get_default_group_by_config';
 import type { Field, StepDefineExposedState } from './types';
-import { isPopulatedObject } from '../../../../../common/utils/object_utils';
+import { isRuntimeMappings } from './types';
 
 const illegalEsAggNameChars = /[[\]>]/g;
 
@@ -77,7 +77,7 @@ export function getPivotDropdownOptions(
 
   // Support for runtime_mappings that are defined by queries
   let runtimeFields: Field[] = [];
-  if (isPopulatedObject(runtimeMappings)) {
+  if (isRuntimeMappings(runtimeMappings)) {
     runtimeFields = Object.keys(runtimeMappings).map((fieldName) => {
       const field = runtimeMappings[fieldName];
       return { name: fieldName, type: getKibanaFieldTypeFromEsType(field.type) };
diff --git a/x-pack/plugins/transform/public/app/sections/create_transform/components/step_define/common/types.test.ts b/x-pack/plugins/transform/public/app/sections/create_transform/components/step_define/common/types.test.ts
new file mode 100644
index 0000000000000..b4948fd65aa2d
--- /dev/null
+++ b/x-pack/plugins/transform/public/app/sections/create_transform/components/step_define/common/types.test.ts
@@ -0,0 +1,51 @@
+/*
+ * Copyright Elasticsearch B.V. and/or licensed to Elasticsearch B.V. under one
+ * or more contributor license agreements. Licensed under the Elastic License
+ * 2.0; you may not use this file except in compliance with the Elastic License
+ * 2.0.
+ */
+
+import { isRuntimeField, isRuntimeMappings } from './types';
+
+describe('Transform: step_define type guards', () => {
+  it('isRuntimeField()', () => {
+    expect(isRuntimeField(1)).toBe(false);
+    expect(isRuntimeField(null)).toBe(false);
+    expect(isRuntimeField([])).toBe(false);
+    expect(isRuntimeField({})).toBe(false);
+    expect(isRuntimeField({ someAttribute: 'someValue' })).toBe(false);
+    expect(isRuntimeField({ type: 'wrong-type' })).toBe(false);
+    expect(isRuntimeField({ type: 'keyword', someAttribute: 'some value' })).toBe(false);
+
+    expect(isRuntimeField({ type: 'keyword' })).toBe(true);
+    expect(isRuntimeField({ type: 'keyword', script: 'some script' })).toBe(true);
+  });
+
+  it('isRuntimeMappings()', () => {
+    expect(isRuntimeMappings(1)).toBe(false);
+    expect(isRuntimeMappings(null)).toBe(false);
+    expect(isRuntimeMappings([])).toBe(false);
+    expect(isRuntimeMappings({})).toBe(false);
+    expect(isRuntimeMappings({ someAttribute: 'someValue' })).toBe(false);
+    expect(isRuntimeMappings({ fieldName1: { type: 'keyword' }, fieldName2: 'someValue' })).toBe(
+      false
+    );
+    expect(
+      isRuntimeMappings({
+        fieldName1: { type: 'keyword' },
+        fieldName2: { type: 'keyword', someAttribute: 'some value' },
+      })
+    ).toBe(false);
+
+    expect(isRuntimeMappings({ fieldName: { type: 'keyword' } })).toBe(true);
+    expect(
+      isRuntimeMappings({ fieldName1: { type: 'keyword' }, fieldName2: { type: 'keyword' } })
+    ).toBe(true);
+    expect(
+      isRuntimeMappings({
+        fieldName1: { type: 'keyword' },
+        fieldName2: { type: 'keyword', script: 'some script' },
+      })
+    ).toBe(true);
+  });
+});
diff --git a/x-pack/plugins/transform/public/app/sections/create_transform/components/step_define/common/types.ts b/x-pack/plugins/transform/public/app/sections/create_transform/components/step_define/common/types.ts
index 6c9293a6d13cf..3fe78a4be84ea 100644
--- a/x-pack/plugins/transform/public/app/sections/create_transform/components/step_define/common/types.ts
+++ b/x-pack/plugins/transform/public/app/sections/create_transform/components/step_define/common/types.ts
@@ -24,6 +24,8 @@ import {
 } from '../../../../../../../common/types/transform';
 import { LatestFunctionConfig } from '../../../../../../../common/api_schemas/transforms';
 
+import { isPopulatedObject } from '../../../../../common/utils/object_utils';
+
 export interface ErrorMessage {
   query: string;
   message: string;
@@ -70,10 +72,25 @@ export interface StepDefineExposedState {
   isRuntimeMappingsEditorEnabled: boolean;
 }
 
+export function isRuntimeField(arg: any): arg is RuntimeField {
+  return (
+    isPopulatedObject(arg) &&
+    ((Object.keys(arg).length === 1 && arg.hasOwnProperty('type')) ||
+      (Object.keys(arg).length === 2 &&
+        arg.hasOwnProperty('type') &&
+        arg.hasOwnProperty('script'))) &&
+    RUNTIME_FIELD_TYPES.includes(arg.type)
+  );
+}
+
+export function isRuntimeMappings(arg: any): arg is RuntimeMappings {
+  return isPopulatedObject(arg) && Object.values(arg).every((d) => isRuntimeField(d));
+}
+
 export function isPivotPartialRequest(arg: any): arg is { pivot: PivotConfigDefinition } {
-  return typeof arg === 'object' && arg.hasOwnProperty('pivot');
+  return isPopulatedObject(arg) && arg.hasOwnProperty('pivot');
 }
 
 export function isLatestPartialRequest(arg: any): arg is { latest: LatestFunctionConfig } {
-  return typeof arg === 'object' && arg.hasOwnProperty('latest');
+  return isPopulatedObject(arg) && arg.hasOwnProperty('latest');
 }