diff --git a/build/buildbot/config/common.xml b/build/buildbot/config/common.xml
index b99af4c177..32c4b821ec 100644
--- a/build/buildbot/config/common.xml
+++ b/build/buildbot/config/common.xml
@@ -60,13 +60,21 @@
 <nightly-schedulers name="daily"/>
 
 <!--
-    General purpose slave lock.
+    A general purpose slave lock and ones for the trunk and stable branches.
 -->
 
 <slavelock>
     <name>slave</name>
 </slavelock>
 
+<slavelock>
+    <name>trunk</name>
+</slavelock>
+
+<slavelock>
+    <name><STABLE_BRANCH/></name>
+</slavelock>
+
 <!--
     Map SVN user ids to email addresses.
 -->
diff --git a/build/buildbot/config/include/xp_vc.xml b/build/buildbot/config/include/xp_vc.xml
index d37ad948dc..e46cbe3814 100644
--- a/build/buildbot/config/include/xp_vc.xml
+++ b/build/buildbot/config/include/xp_vc.xml
@@ -16,12 +16,17 @@
 
 <!--
     build - Override <build> to add a slave lock. This has the effect of
-            serialising all the builds on this machine
+            serialising builds for the same branch on this machine.
 -->
 <xsl:template name="build">
     <xsl:param name="content"/>
+    <xsl:variable name="checkout">
+        <xsl:apply-templates select="get:step('checkout')"/>
+    </xsl:variable>
     <build>
-        <lock>slave</lock>
+        <lock>
+            <xsl:value-of select="exsl:node-set($checkout)/svn/defaultBranch"/>
+        </lock>
         <xsl:copy-of select="$content"/>
     </build>
 </xsl:template>