diff --git a/idea/src/org/jetbrains/kotlin/idea/completion/CompletionSession.kt b/idea/src/org/jetbrains/kotlin/idea/completion/CompletionSession.kt
index 4b266109375..66b888a24f2 100644
--- a/idea/src/org/jetbrains/kotlin/idea/completion/CompletionSession.kt
+++ b/idea/src/org/jetbrains/kotlin/idea/completion/CompletionSession.kt
@@ -286,8 +286,7 @@ class BasicCompletionSession(configuration: CompletionSessionConfiguration,
                 addReferenceVariants(kindFilter, runtimeReceiverType = false)
             }
 
-            val ampIndex = prefix.indexOf("@")
-            val keywordsPrefix = if (ampIndex < 0) prefix else prefix.substring(0, ampIndex) // if there is '@' in the prefix - use shorter prefix to not loose 'this' etc
+            val keywordsPrefix = prefix.substringBefore('@') // if there is '@' in the prefix - use shorter prefix to not loose 'this' etc
             KeywordCompletion.complete(expression ?: parameters.getPosition(), keywordsPrefix) { lookupElement ->
                 val keyword = lookupElement.getLookupString()
                 when (keyword) {
diff --git a/idea/src/org/jetbrains/kotlin/idea/completion/LookupElementFactory.kt b/idea/src/org/jetbrains/kotlin/idea/completion/LookupElementFactory.kt
index 68d5dd886fe..9d9da8d25f6 100644
--- a/idea/src/org/jetbrains/kotlin/idea/completion/LookupElementFactory.kt
+++ b/idea/src/org/jetbrains/kotlin/idea/completion/LookupElementFactory.kt
@@ -110,8 +110,7 @@ public class LookupElementFactory(
         }
 
         val qualifiedName = psiClass.getQualifiedName()!!
-        val dotIndex = qualifiedName.lastIndexOf('.')
-        val packageName = if (dotIndex <= 0) "<root>" else qualifiedName.substring(0, dotIndex)
+        val packageName = qualifiedName.substringBeforeLast('.', "<root>")
         element = element.appendTailText(" ($packageName)", true)
 
         if (psiClass.isDeprecated()) {
diff --git a/j2k/tests/org/jetbrains/kotlin/j2k/AbstractJavaToKotlinConverterSingleFileTest.kt b/j2k/tests/org/jetbrains/kotlin/j2k/AbstractJavaToKotlinConverterSingleFileTest.kt
index 1e71ced1ad6..6a4043ad5a3 100644
--- a/j2k/tests/org/jetbrains/kotlin/j2k/AbstractJavaToKotlinConverterSingleFileTest.kt
+++ b/j2k/tests/org/jetbrains/kotlin/j2k/AbstractJavaToKotlinConverterSingleFileTest.kt
@@ -136,15 +136,9 @@ public abstract class AbstractJavaToKotlinConverterSingleFileTest : AbstractJava
     override fun getProjectDescriptor()
             = JetWithJdkAndRuntimeLightProjectDescriptor.INSTANCE
 
-    private fun String.removeFirstLine(): String {
-        val lastNewLine = indexOf('\n')
-        return if (lastNewLine == -1) "" else substring(lastNewLine)
-    }
+    private fun String.removeFirstLine() = substringAfter('\n', "")
 
-    private fun String.removeLastLine(): String {
-        val lastNewLine = lastIndexOf('\n')
-        return if (lastNewLine == -1) "" else substring(0, lastNewLine)
-    }
+    private fun String.removeLastLine() = substringBeforeLast('\n', "")
 
     private fun createJavaFile(text: String): PsiJavaFile {
         return myFixture.configureByText("converterTestFile.java", text) as PsiJavaFile