diff --git a/PythonAPI/pycocotools/cocoeval.py b/PythonAPI/pycocotools/cocoeval.py
index f4e3decb..9dac015a 100644
--- a/PythonAPI/pycocotools/cocoeval.py
+++ b/PythonAPI/pycocotools/cocoeval.py
@@ -131,6 +131,7 @@ def evaluate(self):
             p.iouType = 'segm' if p.useSegm == 1 else 'bbox'
             print('useSegm (deprecated) is not None. Running {} evaluation'.format(p.iouType))
         print('Evaluate annotation type *{}*'.format(p.iouType))
+        p.imgIds = np.array(p.imgIds, dtype=np.uint)
         p.imgIds = list(np.unique(p.imgIds))
         if p.useCats:
             p.catIds = list(np.unique(p.catIds))