diff --git a/etc/layout_viewer/viewer.html b/etc/layout_viewer/viewer.html
index f76ab56f46d..c173ec2c365 100644
--- a/etc/layout_viewer/viewer.html
+++ b/etc/layout_viewer/viewer.html
@@ -93,7 +93,7 @@
                 if (node.data.base !== undefined) {
                     return node.data.base;
                 }
-                if (node.data.block_flow.base != undefined) {
+                if (node.data.block_flow.base !== undefined) {
                     return node.data.block_flow.base;
                 }
                 throw "Unknown node type";