diff --git a/CHANGELOG.md b/CHANGELOG.md
index 231552c852b..37696011fad 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -6,6 +6,8 @@
 
 - Fixed EuiBasicTable proptypes of itemId ([#3133](https://github.com/elastic/eui/pull/3133))
 - Updated `EuiSuperDatePicker` to inherit the selected value in quick select ([#3105](https://github.com/elastic/eui/pull/3105))
+- Fixed infinite call stack in `EuiResizeObserver`'s fallback polyfill ([#3180](https://github.com/elastic/eui/pull/3180))
+- Correct `defaultProps` definition in `EuiComboBox` ([#3180](https://github.com/elastic/eui/pull/3180))
 
 ### Feature: EuiCollapsibleNav ([#3019](https://github.com/elastic/eui/pull/3019))
 
diff --git a/src/components/combo_box/__snapshots__/combo_box.test.tsx.snap b/src/components/combo_box/__snapshots__/combo_box.test.tsx.snap
index 1fbb44b9711..6d6cedcf6f5 100644
--- a/src/components/combo_box/__snapshots__/combo_box.test.tsx.snap
+++ b/src/components/combo_box/__snapshots__/combo_box.test.tsx.snap
@@ -381,7 +381,6 @@ exports[`props singleSelection is rendered 1`] = `
   role="combobox"
 >
   <EuiComboBoxInput
-    append={null}
     autoSizeInputRef={[Function]}
     compressed={false}
     fullWidth={false}
@@ -396,7 +395,6 @@ exports[`props singleSelection is rendered 1`] = `
     onFocus={[Function]}
     onOpenListClick={[Function]}
     onRemoveOption={[Function]}
-    prepend={null}
     rootId={[Function]}
     searchValue=""
     selectedOptions={
@@ -552,7 +550,6 @@ exports[`props singleSelection selects existing option when opened 1`] = `
   role="combobox"
 >
   <EuiComboBoxInput
-    append={null}
     autoSizeInputRef={[Function]}
     compressed={false}
     fullWidth={false}
@@ -567,7 +564,6 @@ exports[`props singleSelection selects existing option when opened 1`] = `
     onFocus={[Function]}
     onOpenListClick={[Function]}
     onRemoveOption={[Function]}
-    prepend={null}
     rootId={[Function]}
     searchValue=""
     selectedOptions={
diff --git a/src/components/combo_box/combo_box.tsx b/src/components/combo_box/combo_box.tsx
index 7c84e40a528..ebad2f90cd5 100644
--- a/src/components/combo_box/combo_box.tsx
+++ b/src/components/combo_box/combo_box.tsx
@@ -115,7 +115,7 @@ interface _EuiComboBoxProps<T>
    * `startsWith`: moves items that start with search value to top of the list;
    * `none`: don't change the sort order of initial object
    */
-  sortMatchesBy?: 'none' | 'startsWith';
+  sortMatchesBy: 'none' | 'startsWith';
   /**
    * Creates an input group with element(s) coming before input. It won't show if `singleSelection` is set to `false`.
    * `string` | `ReactElement` or an array of these
@@ -178,9 +178,9 @@ export class EuiComboBox<T> extends Component<
     options: [],
     selectedOptions: [],
     singleSelection: false,
-    prepend: null,
-    append: null,
-    sortMatchesBy: 'none',
+    prepend: undefined,
+    append: undefined,
+    sortMatchesBy: 'none' as const,
   };
 
   state: EuiComboBoxState<T> = {
diff --git a/src/components/observer/resize_observer/resize_observer.tsx b/src/components/observer/resize_observer/resize_observer.tsx
index bf10090411e..99f97aee0d2 100644
--- a/src/components/observer/resize_observer/resize_observer.tsx
+++ b/src/components/observer/resize_observer/resize_observer.tsx
@@ -57,9 +57,9 @@ const makeCompatibleObserver = (node: Element, callback: () => void) => {
 
   window.addEventListener('resize', callback);
 
+  const _disconnect = observer.disconnect.bind(observer);
   observer.disconnect = () => {
-    observer.disconnect();
-
+    _disconnect();
     window.removeEventListener('resize', callback);
   };