diff --git a/build.xml b/build.xml
index 9778bb3d260..6436d0c9533 100644
--- a/build.xml
+++ b/build.xml
@@ -304,7 +304,7 @@
             </externs>
         </closure-compiler>
 
-        <jar jarfile="${kotlin-home}/lib/kotlin-jslib.jar">
+        <jar jarfile="${kotlin-home}/lib/kotlin-jslib.jar" duplicate="fail">
             <resources refid="js.lib.files" />
             <zipfileset file="${kotlin-home}/build.txt" prefix="META-INF"/>
             <zipfileset file="${output}/kotlin.js" prefix=""/>
@@ -322,7 +322,7 @@
     </target>
 
     <target name="pack-js-stdlib-sources">
-        <jar destfile="${kotlin-home}/lib/kotlin-jslib-sources.jar">
+        <jar destfile="${kotlin-home}/lib/kotlin-jslib-sources.jar" duplicate="fail">
             <resources refid="js.lib.files" />
             <fileset refid="kotlin.builtin.files" />
 
@@ -759,7 +759,7 @@
     </target>
 
     <target name="pack-runtime-sources">
-        <jar destfile="${kotlin-home}/lib/kotlin-runtime-sources.jar">
+        <jar destfile="${kotlin-home}/lib/kotlin-runtime-sources.jar" duplicate="fail">
             <fileset dir="${basedir}/core/builtins/native" includes="**/*"/>
             <fileset dir="${basedir}/core/builtins/src" includes="**/*"/>
             <fileset dir="${basedir}/core/runtime.jvm/src" includes="**/*"/>
diff --git a/jslib_files.xml b/jslib_files.xml
index ed5a5b8299a..029bdef4875 100644
--- a/jslib_files.xml
+++ b/jslib_files.xml
@@ -29,7 +29,6 @@
             <exclude name="kotlin/io/**" />
             <exclude name="kotlin/math/**" />
             <exclude name="kotlin/template/**" />
-            <exclude name="kotlin/util/**" />
 
             <!-- Temporary disabled -->
             <!--TODO fix: (84, 27) Unresolved reference: copyOf (_SpecialJVM.kt)-->
diff --git a/libraries/stdlib/src/kotlin/AssertionsJVM.kt b/libraries/stdlib/src/kotlin/util/AssertionsJVM.kt
similarity index 100%
rename from libraries/stdlib/src/kotlin/AssertionsJVM.kt
rename to libraries/stdlib/src/kotlin/util/AssertionsJVM.kt
diff --git a/libraries/stdlib/src/kotlin/Functions.kt b/libraries/stdlib/src/kotlin/util/Functions.kt
similarity index 100%
rename from libraries/stdlib/src/kotlin/Functions.kt
rename to libraries/stdlib/src/kotlin/util/Functions.kt
diff --git a/libraries/stdlib/src/kotlin/Integers.kt b/libraries/stdlib/src/kotlin/util/Integers.kt
similarity index 100%
rename from libraries/stdlib/src/kotlin/Integers.kt
rename to libraries/stdlib/src/kotlin/util/Integers.kt
diff --git a/libraries/stdlib/src/kotlin/JLangJVM.kt b/libraries/stdlib/src/kotlin/util/JLangJVM.kt
similarity index 100%
rename from libraries/stdlib/src/kotlin/JLangJVM.kt
rename to libraries/stdlib/src/kotlin/util/JLangJVM.kt
diff --git a/libraries/stdlib/src/kotlin/Numbers.kt b/libraries/stdlib/src/kotlin/util/Numbers.kt
similarity index 100%
rename from libraries/stdlib/src/kotlin/Numbers.kt
rename to libraries/stdlib/src/kotlin/util/Numbers.kt
diff --git a/libraries/stdlib/src/kotlin/Ordering.kt b/libraries/stdlib/src/kotlin/util/Ordering.kt
similarity index 100%
rename from libraries/stdlib/src/kotlin/Ordering.kt
rename to libraries/stdlib/src/kotlin/util/Ordering.kt
diff --git a/libraries/stdlib/src/kotlin/Preconditions.kt b/libraries/stdlib/src/kotlin/util/Preconditions.kt
similarity index 100%
rename from libraries/stdlib/src/kotlin/Preconditions.kt
rename to libraries/stdlib/src/kotlin/util/Preconditions.kt
diff --git a/libraries/stdlib/src/kotlin/Ranges.kt b/libraries/stdlib/src/kotlin/util/Ranges.kt
similarity index 100%
rename from libraries/stdlib/src/kotlin/Ranges.kt
rename to libraries/stdlib/src/kotlin/util/Ranges.kt
diff --git a/libraries/stdlib/src/kotlin/Standard.kt b/libraries/stdlib/src/kotlin/util/Standard.kt
similarity index 100%
rename from libraries/stdlib/src/kotlin/Standard.kt
rename to libraries/stdlib/src/kotlin/util/Standard.kt
diff --git a/libraries/stdlib/src/kotlin/StandardJVM.kt b/libraries/stdlib/src/kotlin/util/StandardJVM.kt
similarity index 100%
rename from libraries/stdlib/src/kotlin/StandardJVM.kt
rename to libraries/stdlib/src/kotlin/util/StandardJVM.kt
diff --git a/libraries/stdlib/src/kotlin/util/System.kt b/libraries/stdlib/src/kotlin/util/SystemJVM.kt
similarity index 100%
rename from libraries/stdlib/src/kotlin/util/System.kt
rename to libraries/stdlib/src/kotlin/util/SystemJVM.kt
diff --git a/libraries/stdlib/src/kotlin/Tuples.kt b/libraries/stdlib/src/kotlin/util/Tuples.kt
similarity index 100%
rename from libraries/stdlib/src/kotlin/Tuples.kt
rename to libraries/stdlib/src/kotlin/util/Tuples.kt