diff --git a/glue/sample/src/sinter/_decoding/_decoding_fusion_blossom.py b/glue/sample/src/sinter/_decoding/_decoding_fusion_blossom.py
index ac3e5bfb..c43760fa 100644
--- a/glue/sample/src/sinter/_decoding/_decoding_fusion_blossom.py
+++ b/glue/sample/src/sinter/_decoding/_decoding_fusion_blossom.py
@@ -24,7 +24,7 @@ def decode_shots_bit_packed(
             bit_packed_detection_event_data: 'np.ndarray',
     ) -> 'np.ndarray':
         num_shots = bit_packed_detection_event_data.shape[0]
-        predictions = np.zeros(shape=(num_shots, self.num_obs), dtype=np.uint8)
+        predictions = np.zeros(shape=(num_shots, (self.num_obs + 7) // 8), dtype=np.uint8)
         import fusion_blossom
         for shot in range(num_shots):
             dets_sparse = np.flatnonzero(np.unpackbits(bit_packed_detection_event_data[shot], count=self.num_dets, bitorder='little'))
diff --git a/glue/sample/src/sinter/_decoding/_decoding_mwpf.py b/glue/sample/src/sinter/_decoding/_decoding_mwpf.py
index 2b69c608..915fd0b0 100644
--- a/glue/sample/src/sinter/_decoding/_decoding_mwpf.py
+++ b/glue/sample/src/sinter/_decoding/_decoding_mwpf.py
@@ -38,7 +38,7 @@ def decode_shots_bit_packed(
         bit_packed_detection_event_data: "np.ndarray",
     ) -> "np.ndarray":
         num_shots = bit_packed_detection_event_data.shape[0]
-        predictions = np.zeros(shape=(num_shots, self.num_obs), dtype=np.uint8)
+        predictions = np.zeros(shape=(num_shots, (self.num_obs + 7) // 8), dtype=np.uint8)
         import mwpf
 
         for shot in range(num_shots):