diff --git a/src/main/java/org/jenkinsci/plugins/uniqueid/implv2/PersistenceRootIdStore.java b/src/main/java/org/jenkinsci/plugins/uniqueid/implv2/PersistenceRootIdStore.java
index 43068ee..e7815a1 100644
--- a/src/main/java/org/jenkinsci/plugins/uniqueid/implv2/PersistenceRootIdStore.java
+++ b/src/main/java/org/jenkinsci/plugins/uniqueid/implv2/PersistenceRootIdStore.java
@@ -42,7 +42,7 @@ public void make(PersistenceRoot object) {
             File tmp = null;
             try {
                 tmp = File.createTempFile(".unique-id_", ".tmp", object.getRootDir());
-                FileUtils.writeStringToFile(f, IdStore.generateUniqueID(), StandardCharsets.UTF_8);
+                FileUtils.writeStringToFile(tmp, IdStore.generateUniqueID(), StandardCharsets.UTF_8);
                 try {
                     Files.move(tmp.toPath(), f.toPath(), StandardCopyOption.ATOMIC_MOVE);
                 }
@@ -62,7 +62,13 @@ public String get(PersistenceRoot object) {
         File f = new File(object.getRootDir(), ID_FILE);
         if (f.exists() && f.canRead()) {
             try {
-                return FileUtils.readFileToString(f, StandardCharsets.UTF_8);
+                String str = FileUtils.readFileToString(f, StandardCharsets.UTF_8);
+                if (str.length() == 0) {
+                    // regenerate it.
+                    make(object);
+                    str = FileUtils.readFileToString(f, StandardCharsets.UTF_8);
+                }
+                return str;
             } catch (IOException ex) {
                 LOGGER.log(Level.WARNING, "Failed to retrieve unique ID for " + object.toString(), ex);
             }
diff --git a/src/test/java/org/jenkinsci/plugins/uniqueid/IdTest.java b/src/test/java/org/jenkinsci/plugins/uniqueid/IdTest.java
index 3885c65..e58aecc 100644
--- a/src/test/java/org/jenkinsci/plugins/uniqueid/IdTest.java
+++ b/src/test/java/org/jenkinsci/plugins/uniqueid/IdTest.java
@@ -1,14 +1,24 @@
 package org.jenkinsci.plugins.uniqueid;
 
-import com.cloudbees.hudson.plugins.folder.Folder;
 import hudson.model.AbstractBuild;
 import hudson.model.AbstractProject;
 import hudson.model.Project;
+
+import java.util.HashSet;
+import java.util.Set;
+
 import org.junit.Rule;
 import org.junit.Test;
 import org.jvnet.hudson.test.JenkinsRule;
 
-import static org.junit.Assert.*;
+import com.cloudbees.hudson.plugins.folder.Folder;
+
+import static org.hamcrest.Matchers.greaterThan;
+import static org.hamcrest.Matchers.hasSize;
+import static org.hamcrest.Matchers.notNullValue;
+import static org.junit.Assert.assertEquals;
+import static org.junit.Assert.assertNull;
+import static org.junit.Assert.assertThat;
 
 public class IdTest {
 
@@ -22,6 +32,10 @@ public void project() throws Exception {
         IdStore.makeId(p);
         String id = IdStore.getId(p);
         AbstractBuild build = jenkinsRule.buildAndAssertSuccess(p);
+        
+        // to be unique we need not null and at least a minimum size.
+        assertThat("project id", id, notNullValue());
+        assertThat("project id", id.length(), greaterThan(20));
 
         // a build will get an id computed from its parent.
         String buildId = IdStore.getId(build);
@@ -44,8 +58,27 @@ public void folder() throws Exception {
         assertNull(IdStore.getId(f));
         IdStore.makeId(f);
         String id = IdStore.getId(f);
+        
+        // to be unique we need not null and at least a minimum size.
+        assertThat("folder id", id, notNullValue());
+        assertThat("folder id", id.length(), greaterThan(20));
+
         jenkinsRule.jenkins.reload();
         assertEquals(id, IdStore.getId(jenkinsRule.jenkins.getItemByFullName("folder", Folder.class)));
-
+    }
+    
+    @Test
+    public void uniqueness() throws Exception {
+        Set<String> ids = new HashSet<String>();
+        for (int i=0;i<100;i++) {
+            Project p = jenkinsRule.createFreeStyleProject();
+            IdStore.makeId(p);
+            ids.add(IdStore.getId(p));
+            
+            Folder f = jenkinsRule.jenkins.createProject(Folder.class, "Folder"+i);
+            IdStore.makeId(f);
+            ids.add(IdStore.getId(f));
+        }
+        assertThat(ids, hasSize(200));
     }
 }