diff --git a/src/internalState/normalizeExpanded.ts b/src/internalState/normalizeExpanded.ts
new file mode 100644
index 0000000..d2363cb
--- /dev/null
+++ b/src/internalState/normalizeExpanded.ts
@@ -0,0 +1,44 @@
+import { useEffect } from 'react';
+import { Store } from 'schummar-state/react';
+import { getAncestors } from '../misc/helpers';
+import { InternalTableState } from '../types';
+
+export function normalizeExpanded<T>(table: Store<InternalTableState<T>>): void {
+  useEffect(
+    () =>
+      table.addReaction(
+        (state) => [state.props.expandOnlyOne, state.expanded, state.itemsById] as const,
+        ([expandOnlyOne, , itemsById], state) => {
+          let expanded = state.expanded;
+          let last, lastItem;
+          let hasChanged = false;
+
+          // If only one branch may be expanded, check if there are more and close if necessary
+          if (expandOnlyOne && (last = [...expanded][expanded.size - 1]) && (lastItem = itemsById.get(last))) {
+            const ancestors = getAncestors(itemsById, lastItem);
+            if ([...expanded].slice(0, -1).some((id) => !ancestors.has(id))) {
+              expanded = state.expanded = new Set([...ancestors].concat(last));
+              hasChanged = true;
+            }
+          } else {
+            for (const id of expanded) {
+              const item = itemsById.get(id);
+              const ancestors = item && getAncestors(itemsById, item);
+              for (const ancestor of ancestors ?? []) {
+                if (!expanded.has(ancestor)) {
+                  expanded.add(ancestor);
+                  hasChanged = true;
+                }
+              }
+            }
+          }
+
+          if (hasChanged) {
+            state.props.onExpandedChange?.(new Set(expanded));
+          }
+        },
+        { runNow: true },
+      ),
+    [table],
+  );
+}
diff --git a/src/internalState/useTableState.ts b/src/internalState/useTableState.ts
index aee8b0c..4cae427 100644
--- a/src/internalState/useTableState.ts
+++ b/src/internalState/useTableState.ts
@@ -6,6 +6,7 @@ import { calcItems } from './calcItems';
 import { calcProps } from './calcProps';
 import { cleanupState } from './cleanupState';
 import { filterColumns } from './filterColumns';
+import { normalizeExpanded } from './normalizeExpanded';
 import { syncSelections } from './syncSelections';
 
 export function useTableState<T>(_props: TableProps<T>): Store<InternalTableState<T>> {
@@ -38,6 +39,7 @@ export function useTableState<T>(_props: TableProps<T>): Store<InternalTableStat
   );
 
   filterColumns(state);
+  normalizeExpanded(state);
   calcItems(state);
   syncSelections(state);
   cleanupState(state);