diff --git a/meshroom/__init__.py b/meshroom/__init__.py
index e2847226..53df30cd 100644
--- a/meshroom/__init__.py
+++ b/meshroom/__init__.py
@@ -78,7 +78,12 @@ def setupEnvironment():
         if not isinstance(val, (list, tuple)):
             val = [val]
 
-        paths[index:index] = val
+        if index == -1:
+            paths.extend(val)
+        elif index == 0:
+            paths = val + paths
+        else:
+            raise ValueError("addToEnvPath: index must be -1 or 0.")
         os.environ[var] = os.pathsep.join(paths)
 
     # setup root directory (override possible by setting "MESHROOM_INSTALL_DIR" environment variable)