diff --git a/core/src/main/java/hudson/FilePath.java b/core/src/main/java/hudson/FilePath.java
index 587dbbf6f4..72089d1e2c 100644
--- a/core/src/main/java/hudson/FilePath.java
+++ b/core/src/main/java/hudson/FilePath.java
@@ -3322,8 +3322,14 @@ public final class FilePath implements Serializable {
             while (!remainingPath.isEmpty()) {
                 Path directChild = this.getDirectChild(currentFilePath, remainingPath);
                 Path childUsingFullPath = currentFilePath.resolve(remainingPath);
-                Path rel = directChild.toAbsolutePath().relativize(childUsingFullPath.toAbsolutePath());
-                remainingPath = rel.toString();
+                String childUsingFullPathAbs = childUsingFullPath.toAbsolutePath().toString();
+                String directChildAbs = directChild.toAbsolutePath().toString();
+
+                if (childUsingFullPathAbs.length() == directChildAbs.length()) {
+                    remainingPath = "";
+                } else {
+                    remainingPath = childUsingFullPathAbs.substring(directChildAbs.length() + 1);
+                }
 
                 File childFileSymbolic = Util.resolveSymlinkToFile(directChild.toFile());
                 if (childFileSymbolic == null) {
diff --git a/core/src/test/java/hudson/FilePathSEC904Test.java b/core/src/test/java/hudson/FilePathSEC904Test.java
index f72050de61..25a3bd3c59 100644
--- a/core/src/test/java/hudson/FilePathSEC904Test.java
+++ b/core/src/test/java/hudson/FilePathSEC904Test.java
@@ -84,6 +84,8 @@ public class FilePathSEC904Test {
         // the intermediate path "./.." goes out of workspace and so is refused
         assertFalse(workspaceFolder.isDescendant("./../workspace"));
         assertFalse(workspaceFolder.isDescendant("./../workspace/"));
+        assertFalse(workspaceFolder.isDescendant(".\\..\\workspace"));
+        assertFalse(workspaceFolder.isDescendant(".\\..\\workspace\\"));
         assertFalse(workspaceFolder.isDescendant("./../workspace/regular.txt"));
         assertFalse(workspaceFolder.isDescendant("../workspace/regular.txt"));
         assertFalse(workspaceFolder.isDescendant("./../../root/workspace/regular.txt"));
@@ -137,8 +139,14 @@ public class FilePathSEC904Test {
         assertTrue(workspaceFolder.isDescendant("_nonexistent"));
         assertTrue(workspaceFolder.isDescendant("a"));
         assertTrue(workspaceFolder.isDescendant("a/a.txt"));
+        assertTrue(workspaceFolder.isDescendant("a/../a/a.txt"));
+        assertTrue(workspaceFolder.isDescendant("b/../a/a.txt"));
         assertTrue(workspaceFolder.isDescendant("b"));
+        assertTrue(workspaceFolder.isDescendant("./b"));
+        assertTrue(workspaceFolder.isDescendant(".\\b"));
         assertTrue(workspaceFolder.isDescendant("b/_a/a.txt"));
+        assertTrue(workspaceFolder.isDescendant("b/_a\\a.txt"));
+        assertTrue(workspaceFolder.isDescendant("b/_a/../a/a.txt"));
         assertTrue(workspaceFolder.isDescendant("b/_atxt"));
         
         // nonexistent but illegal