diff --git a/rolling-shutter/shcryptowasm/shutter_crypto_wasm.go b/rolling-shutter/shcryptowasm/shutter_crypto_wasm.go
index 1b404f6c..f73e7ca0 100644
--- a/rolling-shutter/shcryptowasm/shutter_crypto_wasm.go
+++ b/rolling-shutter/shcryptowasm/shutter_crypto_wasm.go
@@ -147,8 +147,8 @@ func decodeEpochIDArgBytes(arg js.Value) ([]byte, error) {
 	if err != nil {
 		return nil, err
 	}
-	if len(b) != 32 {
-		return nil, fmt.Errorf("sigma must be 32 bytes, got %d", len(b))
+	if len(b) != shcrypto.BlockSize {
+		return nil, fmt.Errorf("epochID must be %d bytes, got %d", shcrypto.BlockSize, len(b))
 	}
 	return b, nil
 }