diff --git a/skimage/restoration/non_local_means.py b/skimage/restoration/non_local_means.py
index f727a12d..6dd20af6 100644
--- a/skimage/restoration/non_local_means.py
+++ b/skimage/restoration/non_local_means.py
@@ -120,6 +120,6 @@ def nl_means_denoising(image, patch_size=7, patch_distance=11, h=0.1,
             return np.array(_nl_means_denoising_2drgb(image, patch_size,
                                 patch_distance, h))
     else:
-        raise ValueError("Non local means denoising is only possible for \
-        2D grayscale and RGB images or 3-D grayscale images.")
+        raise NotImplementedError("Non-local means denoising is only \
+        implemented for 2D grayscale and RGB images or 3-D grayscale images.")
 
diff --git a/skimage/restoration/tests/test_denoise.py b/skimage/restoration/tests/test_denoise.py
index 35e945ec..996c53e3 100644
--- a/skimage/restoration/tests/test_denoise.py
+++ b/skimage/restoration/tests/test_denoise.py
@@ -184,7 +184,7 @@ def test_nl_means_denoising_3d():
 
 def test_nl_means_denoising_wrong_dimension():
     img = np.zeros((5, 5, 5, 5))
-    assert_raises(ValueError, restoration.nl_means_denoising, img)
+    assert_raises(NotImplementedError, restoration.nl_means_denoising, img)
 
 
 if __name__ == "__main__":