diff --git a/common/changes/office-ui-fabric-react/tightenGroupedListTypings_2019-03-26-21-04.json b/common/changes/office-ui-fabric-react/tightenGroupedListTypings_2019-03-26-21-04.json
new file mode 100644
index 0000000000000..ac2cb863b32eb
--- /dev/null
+++ b/common/changes/office-ui-fabric-react/tightenGroupedListTypings_2019-03-26-21-04.json
@@ -0,0 +1,11 @@
+{
+  "changes": [
+    {
+      "packageName": "office-ui-fabric-react",
+      "comment": "GroupHeader: tighten componentWillReceiveProps parameter typing",
+      "type": "patch"
+    }
+  ],
+  "packageName": "office-ui-fabric-react",
+  "email": "naethell@microsoft.com"
+}
\ No newline at end of file
diff --git a/packages/office-ui-fabric-react/src/components/GroupedList/GroupHeader.base.tsx b/packages/office-ui-fabric-react/src/components/GroupedList/GroupHeader.base.tsx
index ce8d200fc1fef..0c955591bae67 100644
--- a/packages/office-ui-fabric-react/src/components/GroupedList/GroupHeader.base.tsx
+++ b/packages/office-ui-fabric-react/src/components/GroupedList/GroupHeader.base.tsx
@@ -31,15 +31,15 @@ export class GroupHeaderBase extends React.Component<IGroupHeaderProps, IGroupHe
     };
   }
 
-  public componentWillReceiveProps(newProps: any): void {
+  public componentWillReceiveProps(newProps: IGroupHeaderProps): void {
     if (newProps.group) {
       const newCollapsed = newProps.group.isCollapsed;
-      const isGroupLoading = newProps.headerProps && newProps.headerProps.isGroupLoading;
+      const isGroupLoading = newProps.isGroupLoading;
       const newLoadingVisible = !newCollapsed && isGroupLoading && isGroupLoading(newProps.group);
 
       this.setState({
-        isCollapsed: newCollapsed,
-        isLoadingVisible: newLoadingVisible
+        isCollapsed: newCollapsed || false,
+        isLoadingVisible: newLoadingVisible || false
       });
     }
   }