diff --git a/modules/kobalt-plugin-api/src/main/kotlin/com/beust/kobalt/internal/TestNgRunner.kt b/modules/kobalt-plugin-api/src/main/kotlin/com/beust/kobalt/internal/TestNgRunner.kt
index e8ea2291..0e1724d2 100644
--- a/modules/kobalt-plugin-api/src/main/kotlin/com/beust/kobalt/internal/TestNgRunner.kt
+++ b/modules/kobalt-plugin-api/src/main/kotlin/com/beust/kobalt/internal/TestNgRunner.kt
@@ -92,7 +92,7 @@ class TestNgRunner : GenericTestRunner() {
         }
 
         val v = Versions.toLongVersion("6.10")
-        val cp = (classpath + dep).map { it.jarFile.get() }
+        val cp = (classpath + dep).distinct().map { it.jarFile.get() }
                 .joinToString(File.pathSeparator)
         val passedArgs = listOf(
                 "-classpath",
diff --git a/modules/kobalt-plugin-api/src/main/kotlin/com/beust/kobalt/misc/Versions.kt b/modules/kobalt-plugin-api/src/main/kotlin/com/beust/kobalt/misc/Versions.kt
index f2141e4d..f915723f 100644
--- a/modules/kobalt-plugin-api/src/main/kotlin/com/beust/kobalt/misc/Versions.kt
+++ b/modules/kobalt-plugin-api/src/main/kotlin/com/beust/kobalt/misc/Versions.kt
@@ -2,10 +2,47 @@ package com.beust.kobalt.misc
 
 import com.beust.kobalt.maven.MavenId
 import com.google.common.base.CharMatcher
+import java.lang.Character
+import java.lang.IllegalStateException
+import java.lang.Integer
+import java.lang.Math
+import java.lang.NumberFormatException
 import java.math.BigInteger
 import java.util.*
 
-public class Versions {
+/**
+ * Allow to compare string versions.
+ */
+class StringVersion(val version: String) {
+    val array = version.split('.')
+
+    enum class Compare { LT, EQ, GT }
+
+    fun compareTo(other: String) : Compare {
+        val s1 = arrayListOf<String>().apply { addAll(version.split('.')) }
+        val s2 = arrayListOf<String>().apply { addAll(other.split('.')) }
+        val max = Math.max(s1.size, s2.size)
+        val shorterList : ArrayList<String> = if (s1.size == max) s2 else s1
+        repeat(max - shorterList.size) {
+            shorterList.add("0")
+        }
+
+        repeat(max) { index ->
+            try {
+                val v1 = Integer.parseInt(s1[index])
+                val v2 = Integer.parseInt(s2[index])
+                if (v1 < v2) return Compare.LT
+                else if (v1 > v2) return Compare.GT
+            } catch(ex: NumberFormatException) {
+                warn("Couldn't parse version $version or $other")
+                return Compare.LT
+            }
+        }
+        return Compare.EQ
+    }
+}
+
+class Versions {
     companion object {
         /**
          * Turn "6.9.4" into 600090004
diff --git a/src/test/kotlin/com/beust/kobalt/internal/VersionTest.kt b/src/test/kotlin/com/beust/kobalt/internal/VersionTest.kt
index 7a6e12b5..ab275e7f 100644
--- a/src/test/kotlin/com/beust/kobalt/internal/VersionTest.kt
+++ b/src/test/kotlin/com/beust/kobalt/internal/VersionTest.kt
@@ -1,10 +1,12 @@
 package com.beust.kobalt.internal
 
+import com.beust.kobalt.misc.StringVersion
 import com.beust.kobalt.misc.Versions
 import org.assertj.core.api.Assertions.assertThat
 import org.testng.annotations.DataProvider
 import org.testng.annotations.Test
 
+
 /**
  * Make sure we parse version numbers correctly.
  */
@@ -22,4 +24,40 @@ class VersionTest {
     fun versionConversionShouldWork(version: String, expected: Long) {
         assertThat(Versions.toLongVersion(version)).isEqualTo(expected)
     }
+
+    @DataProvider
+    fun versionsEqual() : Array<Array<String>>
+        = arrayOf(
+            arrayOf("1", "1"),
+            arrayOf("1.0", "1"),
+            arrayOf("1.0.0", "1"),
+            arrayOf("1.0", "1.0.0")
+    )
+
+    @Test(dataProvider = "versionsEqual")
+    fun versionComparisonsEqual(v1: String, v2: String) {
+        assertThat(StringVersion(v1).compareTo(v2)).isEqualTo(StringVersion.Compare.EQ)
+        assertThat(StringVersion(v2).compareTo(v1)).isEqualTo(StringVersion.Compare.EQ)
+    }
+
+    @DataProvider
+    fun versionsNotEqual() : Array<Array<Any>>
+        = arrayOf(
+            arrayOf("1", "1.2.3", StringVersion.Compare.LT),
+            arrayOf("1.2", "1.2.3", StringVersion.Compare.LT),
+            arrayOf("1.2.2", "1.2.3", StringVersion.Compare.LT),
+            arrayOf("1.2.4", "1.2.3", StringVersion.Compare.GT),
+            arrayOf("1", "1.2.3.4", StringVersion.Compare.LT),
+            arrayOf("1.2", "1.2.3.4", StringVersion.Compare.LT),
+            arrayOf("1.2.3", "1.2.3.4", StringVersion.Compare.LT),
+            arrayOf("1.2.3.3", "1.2.3.4", StringVersion.Compare.LT),
+            arrayOf("1.2.3.5", "1.2.3.4", StringVersion.Compare.GT)
+    )
+
+    @Test(dataProvider = "versionsNotEqual")
+    fun versionComparisonsNotEqual(v1: String, v2: String, expected: StringVersion.Compare) {
+        assertThat(StringVersion(v1).compareTo(v2)).isEqualTo(expected)
+        assertThat(StringVersion(v2).compareTo(v1)).isEqualTo(
+                if (expected == StringVersion.Compare.LT) StringVersion.Compare.GT else StringVersion.Compare.LT)
+    }
 }