diff --git a/pixutils/conv/conv.py b/pixutils/conv/conv.py
index d9ac210..af54c41 100644
--- a/pixutils/conv/conv.py
+++ b/pixutils/conv/conv.py
@@ -100,7 +100,7 @@ def to_bgr888(
     # Get list of backends to try
     backends = get_backends(options.get('backends') if options else None)
     if not backends:
-        raise ValueError('No backends available')
+        raise NotImplementedError('No backends available')
 
     size = 0
 
diff --git a/tests/test_conv.py b/tests/test_conv.py
index 0be13c5..94a6f04 100755
--- a/tests/test_conv.py
+++ b/tests/test_conv.py
@@ -230,10 +230,8 @@ def test_function(self):
             rgb_buf = buffer_to_bgr888(
                 test_case.pixel_format, WIDTH, HEIGHT, 0, src_buf, test_case.options
             )
-        except ValueError as e:
-            if str(e) == 'No backends available':
-                self.skipTest('No backend available')
-            raise
+        except NotImplementedError as e:
+            raise unittest.SkipTest('No backend available') from e
 
         src_sha = hashlib.sha256(src_buf.tobytes()).hexdigest()
         rgb_sha = hashlib.sha256(rgb_buf.tobytes()).hexdigest()
@@ -283,10 +281,8 @@ def test_function(self):
 
         try:
             rgb_buf = buffer_to_bgr888(fmt, WIDTH, HEIGHT, bpl, test_buf, test_case.options)
-        except ValueError as e:
-            if str(e) == 'No backends available':
-                self.skipTest('No backend available')
-            raise
+        except NotImplementedError as e:
+            raise unittest.SkipTest('No backend available') from e
 
         rgb_sha = hashlib.sha256(rgb_buf.tobytes()).hexdigest()
         self.assertEqual(
@@ -345,10 +341,8 @@ def test_function(self):
 
         try:
             rgb_buf = buffer_to_bgr888(fmt, WIDTH, HEIGHT, bpl, test_buf, test_case.options)
-        except ValueError as e:
-            if str(e) == 'No backends available':
-                self.skipTest('No backend available')
-            raise
+        except NotImplementedError as e:
+            raise unittest.SkipTest('No backend available') from e
 
         rgb_sha = hashlib.sha256(rgb_buf.tobytes()).hexdigest()
         self.assertEqual(