diff --git a/snark-document-builder/src/main/kotlin/DocumentBuilder.kt b/snark-document-builder/src/main/kotlin/DocumentBuilder.kt
index 1b1ebe5..fe96f5e 100644
--- a/snark-document-builder/src/main/kotlin/DocumentBuilder.kt
+++ b/snark-document-builder/src/main/kotlin/DocumentBuilder.kt
@@ -4,7 +4,7 @@ import com.fasterxml.jackson.core.io.BigDecimalParser
 import space.kscience.snark.storage.*
 import java.nio.file.Path
 
-val DEFAULT_DOCUMENT_ROOT = "main.md"
+private val DEFAULT_DOCUMENT_ROOT = "main.md"
 
 public suspend fun buildDocument(documentDirectory: Directory) {
     val documentRoot = documentDirectory.get(DEFAULT_DOCUMENT_ROOT)