diff --git a/src/main/java/org/jenkinsci/plugins/vSphereCloudSlaveTemplate.java b/src/main/java/org/jenkinsci/plugins/vSphereCloudSlaveTemplate.java
index e29d6422..9e89e21b 100644
--- a/src/main/java/org/jenkinsci/plugins/vSphereCloudSlaveTemplate.java
+++ b/src/main/java/org/jenkinsci/plugins/vSphereCloudSlaveTemplate.java
@@ -82,7 +82,9 @@ public class vSphereCloudSlaveTemplate implements Describable<vSphereCloudSlaveT
     protected static final SchemeRequirement HTTP_SCHEME = new SchemeRequirement("http");
     protected static final SchemeRequirement HTTPS_SCHEME = new SchemeRequirement("https");
 
-    private final String cloneNamePrefix;
+    private int configVersion;
+    private static final int CURRENT_CONFIG_VERSION = 1;
+    private String cloneNamePrefix; // almost final
     private final String masterImageName;
     private Boolean useSnapshot; // almost final
     private final String snapshotName;
@@ -148,6 +150,7 @@ public vSphereCloudSlaveTemplate(final String cloneNamePrefix,
                                      final RetentionStrategy<?> retentionStrategy,
                                      final List<? extends NodeProperty<?>> nodeProperties,
                                      final List<? extends VSphereGuestInfoProperty> guestInfoProperties) {
+        this.configVersion = CURRENT_CONFIG_VERSION;
         this.cloneNamePrefix = cloneNamePrefix;
         this.masterImageName = masterImageName;
         this.snapshotName = snapshotName;
@@ -349,6 +352,38 @@ protected Object readResolve() {
                 LOGGER.log(Level.CONFIG, " - Failed to reconfigure strategy", ex);
             }
         }
+        // Earlier versions of the code may have stored configuration in a
+        // different way but in the same kind of fields, so we need an explicit
+        // versioning to know how to mutate the data.
+        if (configVersion <= 0) {
+            LOGGER.log(Level.CONFIG,
+                    "{0} loaded old configuration that had hard-coded underscore at the end of the cloneNamePrefix.",
+                    this);
+            // In version one, the underscore was removed from the code so we
+            // have to put it in the data (the user is then free to change it to
+            // something else if they want to).
+            this.cloneNamePrefix = this.cloneNamePrefix + "_";
+            configVersion = 1;
+        }
+        // Note: Subsequent changes dependent on configVersion should go above
+        // this line.
+        if (configVersion < CURRENT_CONFIG_VERSION) {
+            throw new IllegalStateException("Internal error: configVersion==" + configVersion
+                    + " at end of readResolve method, but the current config version should be "
+                    + CURRENT_CONFIG_VERSION
+                    + ".  Either CURRENT_CONFIG_VERSION is incorrect or the readResolve method is not setting configVersion when it upgrades the data.");
+        }
+        if (configVersion > CURRENT_CONFIG_VERSION) {
+            LOGGER.log(Level.WARNING,
+                    "{0} was defined by a later version of the plugin "
+                            + "(one that saved with configVersion={1}, whereas this version of the plugin is expecting {2}).  "
+                            + "The code may not function as expected.",
+                    new Object[]{
+                            this,
+                            configVersion,
+                            CURRENT_CONFIG_VERSION
+                    });
+        }
         return this;
     }
 
diff --git a/src/main/java/org/jenkinsci/plugins/vsphere/tools/CloudProvisioningAlgorithm.java b/src/main/java/org/jenkinsci/plugins/vsphere/tools/CloudProvisioningAlgorithm.java
index 20f37720..de420758 100644
--- a/src/main/java/org/jenkinsci/plugins/vsphere/tools/CloudProvisioningAlgorithm.java
+++ b/src/main/java/org/jenkinsci/plugins/vsphere/tools/CloudProvisioningAlgorithm.java
@@ -44,15 +44,17 @@ public static CloudProvisioningRecord findTemplateWithMostFreeCapacity(
     }
 
     /**
-     * Chooses a name for a new node.
+     * Chooses a name for a new node. The name will start with the
+     * {@link vSphereCloudSlaveTemplate#getCloneNamePrefix()}.
      * <ul>
      * <li>If the template has a limited number of instances available then the
-     * name will be of the form "prefix_number" where "number" is a number that
-     * should be between 1 and the number of permitted instances.</li>
+     * name will be of the form "prefix<i>number</i>" where "<i>number</i>" is a
+     * number that should be between 1 and the number of permitted instances.
+     * </li>
      * <li>If the template has an unlimited number of instances available then
-     * the name will be of the form "prefix_random" where "random" is a random
-     * UUID's 32-byte number (rendered using a high radix to keep the string
-     * short).</li>
+     * the name will be of the form "prefix<i>random</i>" where "<i>random</i>"
+     * is a random UUID's 32-byte (128 bit) number (rendered using a high radix
+     * to keep the string short).</li>
      * </ul>
      * 
      * @param record
@@ -70,7 +72,7 @@ public static String findUnusedName(CloudProvisioningRecord record) {
         final int maxAttempts = hasCap ? (templateInstanceCap) : 100;
         for (int attempt = 0; attempt < maxAttempts; attempt++) {
             final String suffix = hasCap ? calcSequentialSuffix(attempt) : calcRandomSuffix(attempt);
-            final String nodeName = cloneNamePrefix + "_" + suffix;
+            final String nodeName = cloneNamePrefix + suffix;
             if (!existingNames.contains(nodeName)) {
                 return nodeName;
             }
@@ -134,4 +136,4 @@ static BigInteger toBigInteger(final long msb, final long lsb) {
         final BigInteger bigNumber = new BigInteger(bytes);
         return bigNumber;
     }
-}
\ No newline at end of file
+}
diff --git a/src/main/resources/org/jenkinsci/plugins/vSphereCloudSlaveTemplate/help-cloneNamePrefix.html b/src/main/resources/org/jenkinsci/plugins/vSphereCloudSlaveTemplate/help-cloneNamePrefix.html
index 3133efd0..f367da65 100644
--- a/src/main/resources/org/jenkinsci/plugins/vSphereCloudSlaveTemplate/help-cloneNamePrefix.html
+++ b/src/main/resources/org/jenkinsci/plugins/vSphereCloudSlaveTemplate/help-cloneNamePrefix.html
@@ -1,6 +1,6 @@
 <div>
 Controls the name by which the virtual machine will be known to vSphere.
-The plug-in will append an underscore and a unique ID to this prefix in order to generate unique names.<p>
+The plug-in will append a unique ID to this prefix in order to generate unique names.<p>
 Note: You must ensure that no virtual machines (other than those created by this template) have names starting with this prefix.
 </p>
 </div>
\ No newline at end of file
diff --git a/src/test/java/org/jenkinsci/plugins/vsphere/tools/CloudProvisioningAlgorithmTest.java b/src/test/java/org/jenkinsci/plugins/vsphere/tools/CloudProvisioningAlgorithmTest.java
index 785e36fb..02f2af5b 100644
--- a/src/test/java/org/jenkinsci/plugins/vsphere/tools/CloudProvisioningAlgorithmTest.java
+++ b/src/test/java/org/jenkinsci/plugins/vsphere/tools/CloudProvisioningAlgorithmTest.java
@@ -200,8 +200,8 @@ public void findUnusedNameGivenZeroOfTwoExistsThenReturnsOneThenTwo() {
         // Given
         final CloudProvisioningRecord record = createInstance(2, 0, 0);
         final String prefix = record.getTemplate().getCloneNamePrefix();
-        final String expected1 = prefix + "_1";
-        final String expected2 = prefix + "_2";
+        final String expected1 = prefix + "1";
+        final String expected2 = prefix + "2";
 
         // When
         final String actual1 = CloudProvisioningAlgorithm.findUnusedName(record);
@@ -219,10 +219,10 @@ public void findUnusedNameGivenMiddleOfThreeStillExistsThenReturnsOneThenThree()
         // Given
         final CloudProvisioningRecord record = createInstance(3, 0, 0);
         final String prefix = record.getTemplate().getCloneNamePrefix();
-        final String expected1 = prefix + "_1";
-        final String unwanted = prefix + "_2";
+        final String expected1 = prefix + "1";
+        final String unwanted = prefix + "2";
         record.setCurrentlyUnwanted(unwanted, false);
-        final String expected2 = prefix + "_3";
+        final String expected2 = prefix + "3";
 
         // When
         final String actual1 = CloudProvisioningAlgorithm.findUnusedName(record);
@@ -240,9 +240,9 @@ public void findUnusedNameGivenNoSpaceThenThrowsIllegalStateException() {
         // Given
         final CloudProvisioningRecord record = createInstance(3, 0, 0);
         final String prefix = record.getTemplate().getCloneNamePrefix();
-        final String unwanted = prefix + "_1";
-        final String active = prefix + "_2";
-        final String planned = prefix + "_3";
+        final String unwanted = prefix + "1";
+        final String active = prefix + "2";
+        final String planned = prefix + "3";
         record.setCurrentlyUnwanted(unwanted, false);
         record.addCurrentlyActive(active);
         record.addCurrentlyPlanned(planned);
@@ -264,7 +264,7 @@ public void findUnusedNameGivenOneOfTwoHasEndedThenReturnsOne() {
         // Given
         final CloudProvisioningRecord record = createInstance(2, 0, 0);
         final String prefix = record.getTemplate().getCloneNamePrefix();
-        final String expected = prefix + "_1";
+        final String expected = prefix + "1";
 
         // When
         final String actual1 = CloudProvisioningAlgorithm.findUnusedName(record);
@@ -296,7 +296,7 @@ public void findUnusedNameGivenUncappedInstancesThenReturnsUniqueNames() {
         // Then
         final List<String> uniques = new ArrayList<String>(new LinkedHashSet<String>(actuals));
         assertThat(actuals, equalTo(uniques));
-        assertThat(actuals, everyItem(startsWith(prefix + "_")));
+        assertThat(actuals, everyItem(startsWith(prefix)));
     }
 
     private CloudProvisioningRecord createInstance(int capacity, int provisioned, int planned) {