diff --git a/denoising_diffusion_pytorch/denoising_diffusion_pytorch.py b/denoising_diffusion_pytorch/denoising_diffusion_pytorch.py
index 248a59ace..1ce813cbe 100644
--- a/denoising_diffusion_pytorch/denoising_diffusion_pytorch.py
+++ b/denoising_diffusion_pytorch/denoising_diffusion_pytorch.py
@@ -496,6 +496,9 @@ def __init__(
         self.channels = self.model.channels
         self.self_condition = self.model.self_condition
 
+        if isinstance(image_size, int):
+            image_size = (image_size, image_size)
+        assert isinstance(image_size, (tuple, list)) and len(image_size) == 2, 'image size must be a integer or a tuple/list of two integers'
         self.image_size = image_size
 
         self.objective = objective
@@ -729,9 +732,9 @@ def ddim_sample(self, shape, return_all_timesteps = False):
 
     @torch.inference_mode()
     def sample(self, batch_size = 16, return_all_timesteps = False):
-        image_size, channels = self.image_size, self.channels
+        (h, w), channels = self.image_size, self.channels
         sample_fn = self.p_sample_loop if not self.is_ddim_sampling else self.ddim_sample
-        return sample_fn((batch_size, channels, image_size, image_size), return_all_timesteps = return_all_timesteps)
+        return sample_fn((batch_size, channels, h, w), return_all_timesteps = return_all_timesteps)
 
     @torch.inference_mode()
     def interpolate(self, x1, x2, t = None, lam = 0.5):
@@ -811,7 +814,7 @@ def p_losses(self, x_start, t, noise = None, offset_noise_strength = None):
 
     def forward(self, img, *args, **kwargs):
         b, c, h, w, device, img_size, = *img.shape, img.device, self.image_size
-        assert h == img_size and w == img_size, f'height and width of image must be {img_size}'
+        assert h == img_size[0] and w == img_size[1], f'height and width of image must be {img_size}'
         t = torch.randint(0, self.num_timesteps, (b,), device=device).long()
 
         img = self.normalize(img)