diff --git a/shader/pathtag_scan.wgsl b/shader/pathtag_scan.wgsl
index 009e3b4..0d8e9e5 100644
--- a/shader/pathtag_scan.wgsl
+++ b/shader/pathtag_scan.wgsl
@@ -60,6 +60,7 @@ fn main(
         workgroupBarrier();
         sh_monoid[local_id.x] = agg_part;
     }
+    workgroupBarrier();
     // prefix up to this workgroup
 #ifdef small
     var tm = sh_parent[0];
diff --git a/shader/pathtag_scan1.wgsl b/shader/pathtag_scan1.wgsl
index 1d36ab5..13c31c5 100644
--- a/shader/pathtag_scan1.wgsl
+++ b/shader/pathtag_scan1.wgsl
@@ -55,6 +55,7 @@ fn main(
         workgroupBarrier();
         sh_monoid[local_id.x] = agg;
     }
+    workgroupBarrier();
     // prefix up to this workgroup
     var tm = sh_parent[0];
     if local_id.x > 0u {