diff --git a/io_scene_psk_psa/psa/builder.py b/io_scene_psk_psa/psa/builder.py
index 41fe190..903f57e 100644
--- a/io_scene_psk_psa/psa/builder.py
+++ b/io_scene_psk_psa/psa/builder.py
@@ -98,7 +98,7 @@ def build_psa(context: bpy.types.Context, options: PsaBuildOptions) -> Psa:
             psa_bone.parent_index = parent_index
             psa.bones[parent_index].children_count += 1
         except ValueError:
-            psa_bone.parent_index = -1
+            psa_bone.parent_index = 0
 
         if bone.parent is not None:
             rotation = bone.matrix.to_quaternion().conjugated()
diff --git a/io_scene_psk_psa/psk/builder.py b/io_scene_psk_psa/psk/builder.py
index 7925559..4c15380 100644
--- a/io_scene_psk_psa/psk/builder.py
+++ b/io_scene_psk_psa/psk/builder.py
@@ -97,7 +97,7 @@ def build_psk(context, options: PskBuildOptions) -> Psk:
                 psk_bone.parent_index = parent_index
                 psk.bones[parent_index].children_count += 1
             except ValueError:
-                psk_bone.parent_index = -1
+                psk_bone.parent_index = 0
 
             if bone.parent is not None:
                 rotation = bone.matrix.to_quaternion().conjugated()