diff --git a/modules/kobalt-plugin-api/src/main/kotlin/com/beust/kobalt/internal/JvmCompilerPlugin.kt b/modules/kobalt-plugin-api/src/main/kotlin/com/beust/kobalt/internal/JvmCompilerPlugin.kt
index 43a9c6dd..4688d46f 100644
--- a/modules/kobalt-plugin-api/src/main/kotlin/com/beust/kobalt/internal/JvmCompilerPlugin.kt
+++ b/modules/kobalt-plugin-api/src/main/kotlin/com/beust/kobalt/internal/JvmCompilerPlugin.kt
@@ -172,7 +172,10 @@ open class JvmCompilerPlugin @Inject constructor(
                     if (wi.value.sourceSuffixes.contains("java")) ij = wi.index
                     if (wi.value.sourceSuffixes.contains("kt")) ik = wi.index
                 }
-                Collections.swap(result, ik, ij)
+
+                if (ik >= 0 && ij >= 0) {
+                    Collections.swap(result, ik, ij)
+                }
                 return result
             }