diff --git a/src/vs/workbench/api/common/extHostTypes.ts b/src/vs/workbench/api/common/extHostTypes.ts
index bbe6819401705..76ba067a19539 100644
--- a/src/vs/workbench/api/common/extHostTypes.ts
+++ b/src/vs/workbench/api/common/extHostTypes.ts
@@ -2494,10 +2494,23 @@ export class TreeItem {
 	checkboxState?: vscode.TreeItemCheckboxState;
 
 	static isTreeItem(thing: any, extension: IExtensionDescription): thing is TreeItem {
+		const treeItemThing = thing as vscode.TreeItem2;
+
+		if (treeItemThing.checkboxState !== undefined) {
+			checkProposedApiEnabled(extension, 'treeItemCheckbox');
+			const checkbox = isNumber(treeItemThing.checkboxState) ? treeItemThing.checkboxState :
+				isObject(treeItemThing.checkboxState) && isNumber(treeItemThing.checkboxState.state) ? treeItemThing.checkboxState.state : undefined;
+			const tooltip = !isNumber(treeItemThing.checkboxState) && isObject(treeItemThing.checkboxState) ? treeItemThing.checkboxState.tooltip : undefined;
+			if (checkbox === undefined || (checkbox !== TreeItemCheckboxState.Checked && checkbox !== TreeItemCheckboxState.Unchecked) || (tooltip !== undefined && !isString(tooltip))) {
+				console.log('INVALID tree item, invalid checkboxState', treeItemThing.checkboxState);
+				return false;
+			}
+		}
+
 		if (thing instanceof TreeItem) {
 			return true;
 		}
-		const treeItemThing = thing as vscode.TreeItem2;
+
 		if (treeItemThing.label !== undefined && !isString(treeItemThing.label) && !(treeItemThing.label?.label)) {
 			console.log('INVALID tree item, invalid label', treeItemThing.label);
 			return false;
@@ -2541,16 +2554,6 @@ export class TreeItem {
 			console.log('INVALID tree item, invalid accessibilityInformation', treeItemThing.accessibilityInformation);
 			return false;
 		}
-		if (treeItemThing.checkboxState !== undefined) {
-			checkProposedApiEnabled(extension, 'treeItemCheckbox');
-			const checkbox = isNumber(treeItemThing.checkboxState) ? treeItemThing.checkboxState :
-				isObject(treeItemThing.checkboxState) && isNumber(treeItemThing.checkboxState.state) ? treeItemThing.checkboxState.state : undefined;
-			const tooltip = !isNumber(treeItemThing.checkboxState) && isObject(treeItemThing.checkboxState) ? treeItemThing.checkboxState.tooltip : undefined;
-			if (checkbox === undefined || (checkbox !== TreeItemCheckboxState.Checked && checkbox !== TreeItemCheckboxState.Unchecked) || (tooltip !== undefined && !isString(tooltip))) {
-				console.log('INVALID tree item, invalid checkboxState', treeItemThing.checkboxState);
-				return false;
-			}
-		}
 
 		return true;
 	}