diff --git a/src/autosuggest/autosuggest-option.tsx b/src/autosuggest/autosuggest-option.tsx
index ba7682acb0..71cc5603d3 100644
--- a/src/autosuggest/autosuggest-option.tsx
+++ b/src/autosuggest/autosuggest-option.tsx
@@ -108,9 +108,9 @@ const AutosuggestOption = (
   ref: React.Ref<HTMLDivElement>
 ) => {
   const baseProps = getBaseProps(rest);
-  const useEntered = option.type === 'use-entered';
-  const isParent = option.type === 'parent';
-  const isChild = option.type === 'child';
+  const useEntered = option?.type === 'use-entered';
+  const isParent = option?.type === 'parent';
+  const isChild = option?.type === 'child';
   const { throughIndex, inGroupIndex, groupIndex } = getTestOptionIndexes(option) || {};
 
   let optionContent;
diff --git a/src/autosuggest/utils/utils.ts b/src/autosuggest/utils/utils.ts
index 0cc6082f49..7bbe493266 100644
--- a/src/autosuggest/utils/utils.ts
+++ b/src/autosuggest/utils/utils.ts
@@ -5,7 +5,7 @@ import { AutosuggestItem } from '../interfaces';
 type SearchableFields = 'value' | 'label' | 'description' | 'labelTag';
 type SearchableTagFields = 'tags' | 'filteringTags';
 
-const isGroup = (option: AutosuggestItem) => option.type === 'parent';
+const isGroup = (option: AutosuggestItem) => option?.type === 'parent';
 
 const popLastGroup = (options: AutosuggestItem[]) => {
   if (options.length) {
diff --git a/src/button-dropdown/internal.tsx b/src/button-dropdown/internal.tsx
index e616784397..b392d6282d 100644
--- a/src/button-dropdown/internal.tsx
+++ b/src/button-dropdown/internal.tsx
@@ -22,7 +22,7 @@ import {
   GeneratedAnalyticsMetadataButtonDropdownCollapse,
   GeneratedAnalyticsMetadataButtonDropdownExpand,
 } from './analytics-metadata/interfaces.js';
-import { ButtonDropdownProps, InternalButtonDropdownProps } from './interfaces';
+import { ButtonDropdownProps, InternalButtonDropdownProps, InternalItem } from './interfaces';
 import ItemsList from './items-list';
 import { useButtonDropdown } from './utils/use-button-dropdown';
 import { isLinkItem } from './utils/utils.js';
@@ -180,18 +180,20 @@ const InternalButtonDropdown = React.forwardRef(
     const triggerId = useUniqueId('awsui-button-dropdown__trigger');
 
     const triggerHasBadge = () => {
+      const groupKey: keyof ButtonDropdownProps.ItemGroup = 'items';
       const flatItems = items.flatMap(item => {
-        if ('items' in item) {
+        if (groupKey in item) {
           return item.items;
         }
         return item;
       });
 
+      const badgeKey: keyof InternalItem = 'badge';
       return (
         variant === 'icon' &&
         !!flatItems?.find(item => {
-          if ('badge' in item) {
-            return item.badge;
+          if (badgeKey in item) {
+            return (item as InternalItem).badge;
           }
         })
       );
diff --git a/src/button-group/item-element.tsx b/src/button-group/item-element.tsx
index 8cc623e1c1..325dd7e538 100644
--- a/src/button-group/item-element.tsx
+++ b/src/button-group/item-element.tsx
@@ -103,7 +103,8 @@ const ItemElement = forwardRef(
     };
 
     const onClickHandler = (event: CustomEvent<ButtonGroupProps.ItemClickDetails>) => {
-      const hasPopoverFeedback = 'popoverFeedback' in item && item.popoverFeedback;
+      const feedbackKey: keyof ButtonGroupProps.IconButton = 'popoverFeedback';
+      const hasPopoverFeedback = feedbackKey in item && item.popoverFeedback;
 
       if (hasPopoverFeedback) {
         setTooltip({ item: item.id, feedback: true });
diff --git a/src/flashbar/collapsible-flashbar.tsx b/src/flashbar/collapsible-flashbar.tsx
index 60d10a51e6..644ac35f1b 100644
--- a/src/flashbar/collapsible-flashbar.tsx
+++ b/src/flashbar/collapsible-flashbar.tsx
@@ -35,6 +35,8 @@ import {
   getFlashTypeCount,
   getItemColor,
   getVisibleCollapsedItems,
+  isRefObject,
+  isStackableItem,
   StackableItem,
 } from './utils';
 
@@ -214,11 +216,11 @@ export default function CollapsibleFlashbar({ items, style, ...restProps }: Inte
   // we need to use different, more custom and more controlled animations.
   const hasEntered = (item: StackableItem | FlashbarProps.MessageDefinition) =>
     enteringItems.some(_item => _item.id && _item.id === item.id);
-  const hasLeft = (item: StackableItem | FlashbarProps.MessageDefinition) => !('expandedIndex' in item);
+  const hasLeft = (item: StackableItem | FlashbarProps.MessageDefinition) => !isStackableItem(item);
   const hasEnteredOrLeft = (item: StackableItem | FlashbarProps.MessageDefinition) => hasEntered(item) || hasLeft(item);
 
   const showInnerContent = (item: StackableItem | FlashbarProps.MessageDefinition) =>
-    isFlashbarStackExpanded || hasLeft(item) || ('expandedIndex' in item && item.expandedIndex === 0);
+    isFlashbarStackExpanded || hasLeft(item) || (isStackableItem(item) && item.expandedIndex === 0);
 
   const shouldUseStandardAnimation = (item: StackableItem, index: number) => index === 0 && hasEnteredOrLeft(item);
 
@@ -301,11 +303,7 @@ export default function CollapsibleFlashbar({ items, style, ...restProps }: Inte
                       if (shouldUseStandardAnimation(item, index) && transitionRootElement) {
                         if (typeof transitionRootElement === 'function') {
                           transitionRootElement(el);
-                        } else if (
-                          transitionRootElement &&
-                          typeof transitionRootElement === 'object' &&
-                          'current' in transitionRootElement
-                        ) {
+                        } else if (isRefObject(transitionRootElement)) {
                           (transitionRootElement as React.MutableRefObject<HTMLDivElement | null>).current = el;
                         }
                       }
diff --git a/src/flashbar/non-collapsible-flashbar.tsx b/src/flashbar/non-collapsible-flashbar.tsx
index 96cb0015b0..6c33ddb876 100644
--- a/src/flashbar/non-collapsible-flashbar.tsx
+++ b/src/flashbar/non-collapsible-flashbar.tsx
@@ -13,6 +13,7 @@ import { useFlashbar, useFlashbarVisibility } from './common';
 import { TIMEOUT_FOR_ENTERING_ANIMATION } from './constant';
 import { Flash } from './flash';
 import { FlashbarProps, InternalFlashbarProps } from './interfaces';
+import { isRefObject } from './utils';
 
 import styles from './styles.css.js';
 
@@ -121,11 +122,7 @@ export default function NonCollapsibleFlashbar({ items, i18nStrings, style, ...r
           // If there's a transition root element ref, update it too
           if (transitionRootElement && typeof transitionRootElement === 'function') {
             transitionRootElement(el);
-          } else if (
-            transitionRootElement &&
-            typeof transitionRootElement === 'object' &&
-            'current' in transitionRootElement
-          ) {
+          } else if (transitionRootElement && isRefObject(transitionRootElement)) {
             (transitionRootElement as React.MutableRefObject<HTMLDivElement | null>).current = el;
           }
         }}
diff --git a/src/flashbar/utils.ts b/src/flashbar/utils.ts
index efbc35aa22..e9b7ee8f62 100644
--- a/src/flashbar/utils.ts
+++ b/src/flashbar/utils.ts
@@ -1,5 +1,7 @@
 // Copyright Amazon.com, Inc. or its affiliates. All Rights Reserved.
 // SPDX-License-Identifier: Apache-2.0
+import React from 'react';
+
 import { IconProps } from '../icon/interfaces';
 import { FlashbarProps } from './interfaces';
 
@@ -13,6 +15,16 @@ export interface StackableItem extends FlashbarProps.MessageDefinition {
   collapsedIndex?: number;
 }
 
+export function isStackableItem(item: StackableItem | FlashbarProps.MessageDefinition): item is StackableItem {
+  const key: keyof StackableItem = 'expandedIndex';
+  return key in item;
+}
+
+export function isRefObject<T>(ref: unknown): ref is React.RefObject<T> {
+  const key: keyof React.RefObject<T> = 'current';
+  return ref !== null && typeof ref === 'object' && key in ref;
+}
+
 const typesToColors: Record<FlashbarProps.Type, string> = {
   error: 'red',
   info: 'blue',
diff --git a/src/mixed-line-bar-chart/utils.ts b/src/mixed-line-bar-chart/utils.ts
index 0baa16f70c..3f7216c0c5 100644
--- a/src/mixed-line-bar-chart/utils.ts
+++ b/src/mixed-line-bar-chart/utils.ts
@@ -100,13 +100,15 @@ export const getKeyValue = (key: ChartDataTypes) => (key instanceof Date ? key.g
 export function isYThreshold<T>(
   series: MixedLineBarChartProps.ChartSeries<T>
 ): series is MixedLineBarChartProps.YThresholdSeries {
-  return series.type === 'threshold' && 'y' in series;
+  const key: keyof MixedLineBarChartProps.YThresholdSeries = 'y';
+  return series.type === 'threshold' && key in series;
 }
 
 export function isXThreshold<T>(
   series: MixedLineBarChartProps.ChartSeries<T>
 ): series is MixedLineBarChartProps.XThresholdSeries<T> {
-  return series.type === 'threshold' && 'x' in series;
+  const key: keyof MixedLineBarChartProps.XThresholdSeries<T> = 'x';
+  return series.type === 'threshold' && key in series;
 }
 
 export function isDataSeries<T>(
diff --git a/src/side-navigation/util.tsx b/src/side-navigation/util.tsx
index 8f74d5543a..e6750833d0 100644
--- a/src/side-navigation/util.tsx
+++ b/src/side-navigation/util.tsx
@@ -50,14 +50,16 @@ export function checkDuplicateHrefs(items: ReadonlyArray<SideNavigationProps.Ite
     const item = queue.shift()!;
 
     // Check duplicated hrefs
-    if ('href' in item) {
+    const hrefKey: keyof SideNavigationProps.Link = 'href';
+    if (hrefKey in item) {
       if (hrefs.has(item.href)) {
         warnOnce('SideNavigation', `duplicate href in "${item.text}": ${item.href}`);
       }
       hrefs.add(item.href);
     }
 
-    if ('items' in item) {
+    const itemsKey: keyof SideNavigationProps.Section = 'items';
+    if (itemsKey in item) {
       queue.push(...item.items);
     }
   }
diff --git a/src/top-navigation/parts/utility.tsx b/src/top-navigation/parts/utility.tsx
index bf705f9bfd..6fc0df1003 100644
--- a/src/top-navigation/parts/utility.tsx
+++ b/src/top-navigation/parts/utility.tsx
@@ -4,6 +4,7 @@ import React from 'react';
 import clsx from 'clsx';
 
 import { InternalButton } from '../../button/internal';
+import { ButtonDropdownProps } from '../../button-dropdown/interfaces';
 import { isLinkItem } from '../../button-dropdown/utils/utils';
 import InternalIcon from '../../icon/internal';
 import MenuDropdown, { MenuDropdownProps } from '../../internal/components/menu-dropdown';
@@ -133,7 +134,8 @@ function checkSafeUrlRecursively(itemOrGroup: MenuDropdownProps['items']) {
       checkSafeUrl('TopNavigation', item.href);
     }
 
-    if ('items' in item) {
+    const itemsKey: keyof ButtonDropdownProps.ItemGroup = 'items';
+    if (itemsKey in item) {
       checkSafeUrlRecursively(item.items);
     }
   }