diff --git a/tlatools/customBuild.xml b/tlatools/customBuild.xml
index 633a81188e827bdda5b3b55d9babb59e87e7378b..f4565a61b960de12c57ce9dda492beab569134d8 100644
--- a/tlatools/customBuild.xml
+++ b/tlatools/customBuild.xml
@@ -73,7 +73,7 @@
 		</echo>
 		<!-- compile -->
 		<mkdir dir="${class.dir}" />
-		<javac srcdir="${src.dir}" destdir="${class.dir}" debug="true" verbose="false" source="1.5" target="1.5">
+		<javac includeantruntime="false" srcdir="${src.dir}" destdir="${class.dir}" debug="true" verbose="false" source="1.5" target="1.5">
 			<!-- compilerarg value="-Xlint:deprecation"/-->
 			<classpath refid="project.classpath" />
 			<classpath>
@@ -167,7 +167,7 @@
 	<target name="test" description="Executes accompining unit tests" unless="test.skip">
 		<!-- compile unit tests -->
 		<mkdir dir="${test.class.dir}" />
-		<javac srcdir="${test.dir}" destdir="${test.class.dir}" debug="true" verbose="false" source="1.5" target="1.5">
+		<javac includeantruntime="false" srcdir="${test.dir}" destdir="${test.class.dir}" debug="true" verbose="false" source="1.5" target="1.5">
 			<classpath refid="project.classpath" />
 			<classpath>
 				<pathelement location="lib/junit-4.8.2.jar" />
@@ -226,7 +226,7 @@
 	<target name="test-dist" description="Executes accompining unit tests on jar file" depends="dist" unless="test.skip">
 		<!-- compile unit tests -->
 		<mkdir dir="${test.class.dir}" />
-		<javac srcdir="${test.dir}" destdir="${test.class.dir}" debug="true" verbose="false" source="1.5" target="1.5">
+		<javac includeantruntime="false" srcdir="${test.dir}" destdir="${test.class.dir}" debug="true" verbose="false" source="1.5" target="1.5">
 			<classpath refid="project.classpath" />
 			<classpath>
 				<pathelement location="lib/junit-4.8.2.jar" />
@@ -279,7 +279,7 @@
 	<target name="test-dist-long" description="Executes accompining long-running unit tests on jar file" depends="dist" unless="test.skip">
 		<!-- compile unit tests -->
 		<mkdir dir="${test.class.dir}" />
-		<javac srcdir="${test.dir}-long" destdir="${test.class.dir}" debug="true" verbose="false" source="1.5" target="1.5">
+		<javac includeantruntime="false" srcdir="${test.dir}-long" destdir="${test.class.dir}" debug="true" verbose="false" source="1.5" target="1.5">
 			<classpath refid="project.classpath" />
 			<classpath>
 				<pathelement location="lib/junit-4.8.2.jar" />
@@ -333,7 +333,7 @@
 	<target name="test-verify" description="Verifies TLC parts with NASA's pathfinder model checker">
 		<!-- Compile our boilerplate code needed to verify TLC. E.g. the StateQueueVerify creates -->
 		<!-- examplary produces & consumers and a dummy implementation of StateQueue. -->
-		<javac srcdir="${test.dir}-verify" destdir="${test.class.dir}" debug="true" verbose="false">
+		<javac includeantruntime="false" srcdir="${test.dir}-verify" destdir="${test.class.dir}" debug="true" verbose="false">
 			<classpath refid="project.classpath" />
 			<classpath>
 				<pathelement path="${class.dir}" />