diff --git a/extensions/undertow/deployment/src/main/java/io/quarkus/undertow/deployment/UndertowStaticResourcesBuildStep.java b/extensions/undertow/deployment/src/main/java/io/quarkus/undertow/deployment/UndertowStaticResourcesBuildStep.java
index bdc6a79c615d3..251fef006545f 100644
--- a/extensions/undertow/deployment/src/main/java/io/quarkus/undertow/deployment/UndertowStaticResourcesBuildStep.java
+++ b/extensions/undertow/deployment/src/main/java/io/quarkus/undertow/deployment/UndertowStaticResourcesBuildStep.java
@@ -60,7 +60,7 @@ public void accept(Path path) {
                             return;
                         }
                         Path rel = resource.relativize(path);
-                        if (Files.isDirectory(rel)) {
+                        if (Files.isDirectory(path)) {
                             knownDirectories.add(rel.toString());
                         } else {
                             knownFiles.add(rel.toString());