diff --git a/buildScripts/build-support.ant.xml b/buildScripts/build-support.ant.xml
index 107f5f47..d6439cb0 100644
--- a/buildScripts/build-support.ant.xml
+++ b/buildScripts/build-support.ant.xml
@@ -50,7 +50,7 @@ None of these tasks are normally needed, unless modifying how the build works, s
 		<input addproperty="target.jdk">You need to specify the JDK9+ jdk whose jdk.compiler and java.compiler modules are to be converted. Run ant with -Dtarget.jdk=/full/path/here to automate this, or type the path in now (for example: /Library/JavaVirtualMachines/jdk-14.jdk/Contents/Home):</input>
 	</target>
 	
-	<target name="make.javac-patch-jar" depends="-ask.target-jdk" description="to test javac13 on JDK14, for example, you need a jar (not a jmod), to use with --patch-modules. This task makes those.">
+	<target name="make.javac-patch-jar" depends="-ask.target-jdk, -setup.build" description="to test javac13 on JDK14, for example, you need a jar (not a jmod), to use with --patch-modules. This task makes those.">
 		<exec executable="${target.jdk}/bin/java${executable.suffix}" outputproperty="target.javac.version.full" errorproperty="target.javac.version.err">
 			<arg value="--version" />
 		</exec>
diff --git a/buildScripts/compile.ant.xml b/buildScripts/compile.ant.xml
index 047558a5..c456ec75 100644
--- a/buildScripts/compile.ant.xml
+++ b/buildScripts/compile.ant.xml
@@ -27,7 +27,7 @@ This buildfile is part of projectlombok.org. It takes care of compiling and buil
 	<property name="mapstruct-binding.version" value="0.2.0" />
 	
 	<!-- compiles just 'version.java' and runs the produced class file, setting up the various version properties -->
-	<target name="version" depends="ipp.setup, deps.jdk-runtime" description="Shows the version number" unless="lombok.version">
+	<target name="version" depends="ipp.setup, deps.jdk-runtime, -setup.build" description="Shows the version number" unless="lombok.version">
 		<mkdir dir="build/lombok" />
 		<ivy:compile destdir="build/lombok" source="1.5" target="1.5" ecj="true" nowarn="true">
 			<bootclasspath path="${jdk6-rt.loc}" />
@@ -51,7 +51,7 @@ This buildfile is part of projectlombok.org. It takes care of compiling and buil
 		<echo level="info">Lombok version: ${lombok.version} (${lombok.fullversion})</echo>
 	</target>
 	
-	<target name="compile" depends="version, deps" description="Compiles the code">
+	<target name="compile" depends="version, deps, -setup.build" description="Compiles the code">
 		<!--
 			1. Compile stubs.
 			2. Compile lombok-utils.
@@ -218,7 +218,7 @@ lombok.launch.AnnotationProcessorHider$ClaimingProcessor,isolating</echo>
 	</target>
 	
 	<!-- compiles the bit of API from mapstruct that lombok compiles against. -->
-	<target name="mapstruct.compile">
+	<target name="mapstruct.compile" depends="-setup.build">
 		<mkdir dir="build/mapstruct" />
 		<ivy:compile destdir="build/mapstruct" release="8">
 			<src path="src/j9stubs" />
@@ -294,7 +294,7 @@ lombok.launch.AnnotationProcessorHider$ClaimingProcessor,isolating</echo>
 		<property name="lombok.dist.built" value="true" />
 	</target>
 	
-	<target name="compile.support" depends="ipp.setup, deps" description="Compiles code that is used solely by the build, such as website and IDE project creation">
+	<target name="compile.support" depends="ipp.setup, deps, -setup.build" description="Compiles code that is used solely by the build, such as website and IDE project creation">
 		<ivy:compile includeDestClasses="false" includeantruntime="false" destdir="build/support" debug="on" source="1.8" target="1.8">
 			<compilerarg value="-proc:none" />
 			<compilerarg value="-Xlint:-options" />
diff --git a/buildScripts/mapstructBinding.ant.xml b/buildScripts/mapstructBinding.ant.xml
index a78c5351..d7c52dc3 100644
--- a/buildScripts/mapstructBinding.ant.xml
+++ b/buildScripts/mapstructBinding.ant.xml
@@ -26,7 +26,7 @@ version on mavencentral is the last version that is ever needed; the code itself
 exists as a separate dependency solely because it is itself dependent on both lombok and mapstruct.
 	</description>
 	
-	<target name="-mapstructBinding.compile">
+	<target name="-mapstructBinding.compile" depends="-setup.build">
 		<mkdir dir="build/mapstruct" />
 		<javac includeAntRuntime="false" source="1.8" target="1.8" destdir="build/mapstruct">
 			<src path="src/j9stubs" />
diff --git a/buildScripts/maven.ant.xml b/buildScripts/maven.ant.xml
index dcba2ccb..57bb6b99 100644
--- a/buildScripts/maven.ant.xml
+++ b/buildScripts/maven.ant.xml
@@ -59,7 +59,7 @@ This buildfile is part of projectlombok.org. It makes maven-compatible repositor
 		</sequential>
 	</macrodef>
 	
-	<target name="maven" depends="version, dist, javadoc.build" description="Creates a maven repo for the current release into a build dir. The intent is for you to put that on a server someplace. Will invoke your local mvn installation.">
+	<target name="maven" depends="version, dist, javadoc.build, -setup.build" description="Creates a maven repo for the current release into a build dir. The intent is for you to put that on a server someplace. Will invoke your local mvn installation.">
 		<mkdir dir="build" />
 		<mkdir dir="dist" />
 		
diff --git a/buildScripts/setup.ant.xml b/buildScripts/setup.ant.xml
index ed835960..7875f27d 100644
--- a/buildScripts/setup.ant.xml
+++ b/buildScripts/setup.ant.xml
@@ -24,6 +24,9 @@
 This buildfile is part of projectlombok.org. It sets up the build itself.
 	</description>
 	
+	<!-- increment this number to force a clean of the 'build' dir -->
+	<property name="build.version" value="1" />
+	
 	<property name="pattern.jdk11plus" value="^(\d\d\d+|1[1-9]|[2-9]\d)(\..*)?$" />
 	<property name="ivy.retrieve.pattern" value="lib/[conf]/[organisation]-[artifact].[ext]" />
 	<property environment="env" />
@@ -84,6 +87,37 @@ This buildfile is part of projectlombok.org. It sets up the build itself.
 	
 	<target name="setup.ssh" depends="-setup.ssh.ask, -setup.ssh.save" />
 	
+	<target name="-autoclean.check">
+		<available type="dir" file="build" property="existingbuild.present" />
+		<loadresource property="existingbuild.ver">
+			<first count="1">
+				<resources>
+					<restrict>
+						<fileset dir="." includes="build/build-ver.txt" />
+						<exists />
+					</restrict>
+					<string>0</string>
+				</resources>
+			</first>
+		</loadresource>
+		<condition property="existingbuild.mismatch">
+			<and>
+				<isset property="existingbuild.present" />
+				<not><equals arg1="${existingbuild.ver}" arg2="${build.version}" trim="true" /></not>
+			</and>
+		</condition>
+	</target>
+	
+	<target name="autoclean" depends="-autoclean.check" if="existingbuild.mismatch" description="Checks if a change in the build or deplist neccessitates a clean">
+		<echo>build ver has been incremented, neccessitating a clean...</echo>
+		<delete dir="build" />
+	</target>
+	
+	<target name="-setup.build" depends="autoclean">
+		<mkdir dir="build" />
+		<echo file="build/build-ver.txt">${build.version}</echo>
+	</target>
+	
 	<target name="clean" description="Removes all generated files.">
 		<delete dir="build" quiet="true" />
 	</target>