diff --git a/core/util.runtime/src/org/jetbrains/kotlin/utils/addToStdlib.kt b/core/util.runtime/src/org/jetbrains/kotlin/utils/addToStdlib.kt
index 9fc250e2696..6f5c160e83b 100644
--- a/core/util.runtime/src/org/jetbrains/kotlin/utils/addToStdlib.kt
+++ b/core/util.runtime/src/org/jetbrains/kotlin/utils/addToStdlib.kt
@@ -95,7 +95,7 @@ private val constantMap = ConcurrentHashMap<Function0<*>, Any>()
 fun String.indexOfOrNull(char: Char, startIndex: Int = 0, ignoreCase: Boolean = false): Int? =
         indexOf(char, startIndex, ignoreCase).takeIf { it >= 0 }
 
-fun String.lastIndexOfOrNull(char: Char, startIndex: Int = 0, ignoreCase: Boolean = false): Int? =
+fun String.lastIndexOfOrNull(char: Char, startIndex: Int = lastIndex, ignoreCase: Boolean = false): Int? =
         lastIndexOf(char, startIndex, ignoreCase).takeIf { it >= 0 }
 
 inline fun <T, R : Any> Iterable<T>.firstNotNullResult(transform: (T) -> R?): R? {
diff --git a/idea/idea-gradle/src/org/jetbrains/kotlin/idea/scripting/gradle/roots/GradleBuildRootsManager.kt b/idea/idea-gradle/src/org/jetbrains/kotlin/idea/scripting/gradle/roots/GradleBuildRootsManager.kt
index b5c660e359e..38bd6bacb47 100644
--- a/idea/idea-gradle/src/org/jetbrains/kotlin/idea/scripting/gradle/roots/GradleBuildRootsManager.kt
+++ b/idea/idea-gradle/src/org/jetbrains/kotlin/idea/scripting/gradle/roots/GradleBuildRootsManager.kt
@@ -140,8 +140,8 @@ class GradleBuildRootsManager(val project: Project) : ScriptingSupport.Provider(
             return roots.getBuildByProjectDir(filePath.substringBeforeLast("/"))
         } else if (filePath.endsWith("/gradle-wrapper.properties")) {
             val gradleWrapperDirIndex = filePath.lastIndexOfOrNull('/') ?: return null
-            val gradleDirIndex = filePath.lastIndexOfOrNull('/', gradleWrapperDirIndex) ?: return null
-            val buildDirIndex = filePath.lastIndexOfOrNull('/', gradleDirIndex) ?: return null
+            val gradleDirIndex = filePath.lastIndexOfOrNull('/', gradleWrapperDirIndex - 1) ?: return null
+            val buildDirIndex = filePath.lastIndexOfOrNull('/', gradleDirIndex - 1) ?: return null
             return roots.getBuildByRootDir(filePath.substring(0, buildDirIndex))
         }