diff --git a/src/Collapse.tsx b/src/Collapse.tsx
index 4e2b9ee..79545f4 100644
--- a/src/Collapse.tsx
+++ b/src/Collapse.tsx
@@ -34,9 +34,12 @@ class Collapse extends React.Component<CollapseProps, CollapseState> {
     const { activeKey, defaultActiveKey } = props;
     let currentActiveKey = defaultActiveKey;
     if ('activeKey' in props) {
-      currentActiveKey = activeKey;
+      if (activeKey === 'unset') {
+        currentActiveKey = defaultActiveKey;
+      } else {
+        currentActiveKey = activeKey;
+      }
     }
-
     this.state = {
       activeKey: getActiveKeysArray(currentActiveKey),
     };