diff --git a/appveyor.yml b/appveyor.yml
index ef557d6978..cc9f6515a4 100644
--- a/appveyor.yml
+++ b/appveyor.yml
@@ -10,7 +10,7 @@ matrix:
   fast_finish: true
 
 environment:
-  OSGEO4W_ROOT: C:\OSGeo4W64
+  OSGEO4W_ROOT: C:\\OSGeo4W64
 
   matrix:
     - PDAL_OPTIONAL_COMPONENTS: OFF