diff --git a/core/src/main/java/hudson/model/User.java b/core/src/main/java/hudson/model/User.java
index 222c69e2ef3cdd0b19e1aa45c472fc6b306377ad..8fba2fed291348bcb2e9bd7eddc326d9e11892e3 100644
--- a/core/src/main/java/hudson/model/User.java
+++ b/core/src/main/java/hudson/model/User.java
@@ -459,6 +459,7 @@ public class User extends AbstractModelObject implements AccessControlled, Descr
      * Gets all the users.
      */
     public static Collection<User> getAll() {
+        final IdStrategy strategy = idStrategy();
         if(System.currentTimeMillis() -lastScanned>10000) {
             // occasionally scan the file system to check new users
             // whether we should do this only once at start up or not is debatable.
@@ -471,7 +472,7 @@ public class User extends AbstractModelObject implements AccessControlled, Descr
 
             for (File subdir : subdirs)
                 if(new File(subdir,"config.xml").exists()) {
-                    String name = subdir.getName();
+                    String name = strategy.idFromFilename(subdir.getName());
                     User.getOrCreate(name, name, true);
                 }
 
@@ -486,7 +487,6 @@ public class User extends AbstractModelObject implements AccessControlled, Descr
             byNameLock.readLock().unlock();
         }
         Collections.sort(r,new Comparator<User>() {
-            IdStrategy strategy = idStrategy();
 
             public int compare(User o1, User o2) {
                 return strategy.compare(o1.getId(), o2.getId());
diff --git a/core/src/main/java/jenkins/model/IdStrategy.java b/core/src/main/java/jenkins/model/IdStrategy.java
index 1e4e462db28a8ffe5a08a3f76b3ddbd5fb63ab0a..8ccf691898e2eafe9e17f0476256201ff425356b 100644
--- a/core/src/main/java/jenkins/model/IdStrategy.java
+++ b/core/src/main/java/jenkins/model/IdStrategy.java
@@ -57,6 +57,16 @@ public abstract class IdStrategy extends AbstractDescribableImpl<IdStrategy> imp
     @Nonnull
     public abstract String filenameOf(@Nonnull String id);
 
+    /**
+     * Converts a filename into the corresponding id.
+     * @param filename the filename.
+     * @return the corresponding id.
+     * @since 1.577
+     */
+    public String idFromFilename(@Nonnull String filename) {
+        return filename;
+    }
+
     /**
      * Converts an ID into a key for use in a Java Map.
      *
@@ -214,6 +224,59 @@ public abstract class IdStrategy extends AbstractDescribableImpl<IdStrategy> imp
             }
         }
 
+        @Override
+        public String idFromFilename(@Nonnull String filename) {
+            if (filename.matches("[a-z0-9_. -]+")) {
+                return filename;
+            } else {
+                StringBuilder buf = new StringBuilder(filename.length());
+                final char[] chars = filename.toCharArray();
+                for (int i = 0; i < chars.length; i++) {
+                    char c = chars[i];
+                    if ('a' <= c && c <= 'z') {
+                        buf.append(c);
+                    } else if ('0' <= c && c <= '9') {
+                        buf.append(c);
+                    } else if ('_' == c || '.' == c || '-' == c || ' ' == c || '@' == c) {
+                        buf.append(c);
+                    } else if (c == '~') {
+                        i++;
+                        if (i < chars.length) {
+                            buf.append(Character.toUpperCase(chars[i]));
+                        }
+                    } else if (c == '$') {
+                        StringBuilder hex = new StringBuilder(4);
+                        i++;
+                        if (i < chars.length) {
+                            hex.append(chars[i]);
+                        } else {
+                            break;
+                        }
+                        i++;
+                        if (i < chars.length) {
+                            hex.append(chars[i]);
+                        } else {
+                            break;
+                        }
+                        i++;
+                        if (i < chars.length) {
+                            hex.append(chars[i]);
+                        } else {
+                            break;
+                        }
+                        i++;
+                        if (i < chars.length) {
+                            hex.append(chars[i]);
+                        } else {
+                            break;
+                        }
+                        buf.append(Character.valueOf((char)Integer.parseInt(hex.toString(), 16)));
+                    }
+                }
+                return buf.toString();
+            }
+        }
+
         /**
          * {@inheritDoc}
          */
diff --git a/test/src/test/java/hudson/model/UserTest.java b/test/src/test/java/hudson/model/UserTest.java
index 096ed08a410828b584561a7b71db6c2a59075439..f84bc421fd45dde25711a82c3dd2511927d8a4b8 100644
--- a/test/src/test/java/hudson/model/UserTest.java
+++ b/test/src/test/java/hudson/model/UserTest.java
@@ -174,6 +174,8 @@ public class UserTest {
         User user = User.get("john smith");
         User user2 = User.get("John Smith");
         assertSame("Users should have the same id.", user.getId(), user2.getId());
+        assertEquals(user.getId(), User.idStrategy().idFromFilename(User.idStrategy().filenameOf(user.getId())));
+        assertEquals(user2.getId(), User.idStrategy().idFromFilename(User.idStrategy().filenameOf(user2.getId())));
     }
     
     @Test
@@ -191,6 +193,8 @@ public class UserTest {
         assertEquals("john smith", User.idStrategy().filenameOf(user.getId()));
         assertEquals("John Smith", User.idStrategy().keyFor(user2.getId()));
         assertEquals("~john ~smith", User.idStrategy().filenameOf(user2.getId()));
+        assertEquals(user.getId(), User.idStrategy().idFromFilename(User.idStrategy().filenameOf(user.getId())));
+        assertEquals(user2.getId(), User.idStrategy().idFromFilename(User.idStrategy().filenameOf(user2.getId())));
     }
 
     @Test
@@ -212,6 +216,8 @@ public class UserTest {
         assertEquals("Users should have the same id.", user.getId(), user2.getId());
         assertEquals("john.smith@acme.org", User.idStrategy().keyFor(user2.getId()));
         assertEquals("john.smith@acme.org", User.idStrategy().filenameOf(user2.getId()));
+        assertEquals(user.getId(), User.idStrategy().idFromFilename(User.idStrategy().filenameOf(user.getId())));
+        assertEquals(user2.getId(), User.idStrategy().idFromFilename(User.idStrategy().filenameOf(user2.getId())));
     }
 
     @Test