diff --git a/rapids/models.py b/rapids/models.py
index 0925d5d0..d67a33f2 100644
--- a/rapids/models.py
+++ b/rapids/models.py
@@ -459,7 +459,7 @@ class RapidImage(models.Model):
             try:
                 # and generate a hash from the pixel data
                 dataset = pydicom.dcmread(self.image)
-                hash = hashlib.md5(",".join(str(dataset.pixel_array.tostring()))).hexdigest()
+                hash = hashlib.md5(",".join([str(i) for i in dataset.pixel_array.tostring()])).hexdigest()
                 self.is_dicom = True
             except pydicom.errors.InvalidDicomError:
                 self.image.file.open()