diff --git a/endorsedLibraries/kotlinx.cli/src/main/kotlin/kotlinx/cli/ArgParser.kt b/endorsedLibraries/kotlinx.cli/src/main/kotlin/kotlinx/cli/ArgParser.kt
index 69101439071..ef6a435a84b 100644
--- a/endorsedLibraries/kotlinx.cli/src/main/kotlin/kotlinx/cli/ArgParser.kt
+++ b/endorsedLibraries/kotlinx.cli/src/main/kotlin/kotlinx/cli/ArgParser.kt
@@ -180,14 +180,14 @@ open class ArgParser(val programName: String, var useDefaultHelpShortName: Boole
                 // Previous argument has default value.
                 it.descriptor.defaultValue?.let {
                     if (currentArgument.descriptor.defaultValue == null && currentArgument.descriptor.required) {
-                        printWarning("Default value of argument ${previousArgument.descriptor.fullName} will be unused,  " +
+                        printError("Default value of argument ${previousArgument.descriptor.fullName} will be unused,  " +
                                 "because next argument ${currentArgument.descriptor.fullName} is always required and has no default value.")
                     }
                 }
                 // Previous argument is optional.
                 if (!it.descriptor.required) {
                     if (currentArgument.descriptor.defaultValue == null && currentArgument.descriptor.required) {
-                        printWarning("Argument ${previousArgument.descriptor.fullName} will be always required, " +
+                        printError("Argument ${previousArgument.descriptor.fullName} will be always required, " +
                                 "because next argument ${currentArgument.descriptor.fullName} is always required.")
                     }
                 }
@@ -313,7 +313,7 @@ open class ArgParser(val programName: String, var useDefaultHelpShortName: Boole
 
         // Add default list with arguments if there can be extra free arguments.
         if (skipExtraArguments) {
-            argument(ArgType.String, "").number()
+            argument(ArgType.String, "").vararg()
         }
 
         // Map declared options and arguments to maps.
diff --git a/endorsedLibraries/kotlinx.cli/src/main/kotlin/kotlinx/cli/Arguments.kt b/endorsedLibraries/kotlinx.cli/src/main/kotlin/kotlinx/cli/Arguments.kt
index 45049cc6df9..9e3478e4b1c 100644
--- a/endorsedLibraries/kotlinx.cli/src/main/kotlin/kotlinx/cli/Arguments.kt
+++ b/endorsedLibraries/kotlinx.cli/src/main/kotlin/kotlinx/cli/Arguments.kt
@@ -87,7 +87,7 @@ class SingleNullableArgument<T : Any> internal constructor(descriptor: ArgDescri
 class MultipleArgument<T : Any> internal constructor(descriptor: ArgDescriptor<T, List<T>>, owner: CLIEntityWrapper):
         Argument<List<T>>(owner) {
     init {
-        if (descriptor.number != null && descriptor.number == 1) {
+        if (descriptor.number != null && descriptor.number < 2) {
             failAssertion("Argument with multiple values can't be initialized with descriptor for single one.")
         }
         delegate = ArgumentMultipleValues(descriptor)
@@ -97,11 +97,11 @@ class MultipleArgument<T : Any> internal constructor(descriptor: ArgDescriptor<T
 /**
  * Allow argument have several values.
  *
- * @param number number of arguments are expected. In case of null value any number of arguments can be set.
+ * @param value number of arguments are expected.
  */
-fun <T : Any, TResult> AbstractSingleArgument<T, TResult>.number(value: Int? = null): MultipleArgument<T> {
-    if (value != null && value == 1) {
-        error("number() modifier with value 1 is unavailable. It's already set to 1.")
+fun <T : Any, TResult> AbstractSingleArgument<T, TResult>.multiple(value: Int): MultipleArgument<T> {
+    if (value < 2) {
+        error("multiple() modifier with value less than 2 is unavailable. It's already set to 1.")
     }
     val newArgument = with((delegate as ParsingValue<T, T>).descriptor as ArgDescriptor) {
         MultipleArgument(ArgDescriptor(type, fullName, value, description, listOfNotNull(defaultValue),
@@ -111,6 +111,18 @@ fun <T : Any, TResult> AbstractSingleArgument<T, TResult>.number(value: Int? = n
     return newArgument
 }
 
+/**
+ * Allow argument have several values.
+ */
+fun <T : Any, TResult> AbstractSingleArgument<T, TResult>.vararg(): MultipleArgument<T> {
+    val newArgument = with((delegate as ParsingValue<T, T>).descriptor as ArgDescriptor) {
+        MultipleArgument(ArgDescriptor(type, fullName, null, description, listOfNotNull(defaultValue),
+                required, deprecatedWarning), owner)
+    }
+    owner.entity = newArgument
+    return newArgument
+}
+
 /**
  * Set default value for argument.
  *
@@ -130,6 +142,9 @@ fun <T: Any, TResult> AbstractSingleArgument<T, TResult>.default(value: T): Sing
  * @param value default value.
  */
 fun <T: Any> MultipleArgument<T>.default(value: Collection<T>): MultipleArgument<T> {
+    if (value.isEmpty()) {
+        error("Default value for argument can't be empty collection.")
+    }
     val newArgument = with((delegate as ParsingValue<T, List<T>>).descriptor as ArgDescriptor) {
         MultipleArgument(ArgDescriptor(type, fullName, number, description, value.toList(),
                 required, deprecatedWarning), owner)
@@ -141,7 +156,7 @@ fun <T: Any> MultipleArgument<T>.default(value: Collection<T>): MultipleArgument
 /**
  * Allow argument be unprovided in command line.
  */
-fun <T: Any, TResult> AbstractSingleArgument<T, TResult>.optional(): SingleNullableArgument<T> {
+fun <T: Any> SingleArgument<T>.optional(): SingleNullableArgument<T> {
     val newArgument = with((delegate as ParsingValue<T, T>).descriptor as ArgDescriptor) {
         SingleNullableArgument(ArgDescriptor(type, fullName, number, description, defaultValue,
                 false, deprecatedWarning), owner)
diff --git a/endorsedLibraries/kotlinx.cli/src/main/kotlin/kotlinx/cli/Descriptors.kt b/endorsedLibraries/kotlinx.cli/src/main/kotlin/kotlinx/cli/Descriptors.kt
index 05965d287d1..5d3eb05d820 100644
--- a/endorsedLibraries/kotlinx.cli/src/main/kotlin/kotlinx/cli/Descriptors.kt
+++ b/endorsedLibraries/kotlinx.cli/src/main/kotlin/kotlinx/cli/Descriptors.kt
@@ -127,7 +127,7 @@ internal class ArgDescriptor<T : Any, TResult>(
     init {
         // Check arguments number correctness.
         number?.let {
-            if (it < 0)
+            if (it < 1)
                 error("Number of arguments for argument description $fullName should be greater than zero.")
         }
     }
diff --git a/endorsedLibraries/kotlinx.cli/src/main/kotlin/kotlinx/cli/Options.kt b/endorsedLibraries/kotlinx.cli/src/main/kotlin/kotlinx/cli/Options.kt
index d9d598a8554..cc1088fe658 100644
--- a/endorsedLibraries/kotlinx.cli/src/main/kotlin/kotlinx/cli/Options.kt
+++ b/endorsedLibraries/kotlinx.cli/src/main/kotlin/kotlinx/cli/Options.kt
@@ -116,9 +116,6 @@ fun <T : Any> MultipleOption<T, DelimitedOption>.multiple(): MultipleOption<T, R
  */
 fun <T: Any, TResult> AbstractSingleOption<T, TResult>.default(value: T): SingleOption<T> {
     val newOption = with((delegate as ParsingValue<T, T>).descriptor as OptionDescriptor) {
-        if (required) {
-            printWarning("required() is unneeded, because option with default value is defined.")
-        }
         SingleOption(OptionDescriptor(optionFullFormPrefix, optionShortFromPrefix, type, fullName, shortName,
                 description, value, required, multiple, delimiter, deprecatedWarning), owner)
     }
@@ -134,8 +131,8 @@ fun <T: Any, TResult> AbstractSingleOption<T, TResult>.default(value: T): Single
 fun <T: Any, OptionType: MultipleOptionType>
         MultipleOption<T, OptionType>.default(value: Collection<T>): MultipleOption<T, OptionType> {
     val newOption = with((delegate as ParsingValue<T, List<T>>).descriptor as OptionDescriptor) {
-        if (required) {
-            printWarning("required() is unneeded, because option with default value is defined.")
+        if (value.isEmpty()) {
+            error("Default value for option can't be empty collection.")
         }
         MultipleOption<T, OptionType>(OptionDescriptor(optionFullFormPrefix, optionShortFromPrefix, type, fullName,
                 shortName, description, value.toList(),
@@ -148,11 +145,8 @@ fun <T: Any, OptionType: MultipleOptionType>
 /**
  * Require option to be always provided in command line.
  */
-fun <T: Any, TResult> AbstractSingleOption<T, TResult>.required(): SingleOption<T> {
+fun <T: Any> SingleNullableOption<T>.required(): SingleOption<T> {
     val newOption = with((delegate as ParsingValue<T, T>).descriptor as OptionDescriptor) {
-        defaultValue?.let {
-            printWarning("required() is unneeded, because option with default value is defined.")
-        }
         SingleOption(OptionDescriptor(optionFullFormPrefix, optionShortFromPrefix, type, fullName,
                 shortName, description, defaultValue,
                 true, multiple, delimiter, deprecatedWarning), owner)
@@ -167,9 +161,6 @@ fun <T: Any, TResult> AbstractSingleOption<T, TResult>.required(): SingleOption<
 fun <T: Any, OptionType: MultipleOptionType>
         MultipleOption<T, OptionType>.required(): MultipleOption<T, OptionType> {
     val newOption = with((delegate as ParsingValue<T, List<T>>).descriptor as OptionDescriptor) {
-        if (required) {
-            printWarning("required() is unneeded, because option with default value is defined.")
-        }
         MultipleOption<T, OptionType>(OptionDescriptor(optionFullFormPrefix, optionShortFromPrefix, type, fullName, shortName,
                 description, defaultValue?.toList() ?: listOf(),
                 true, multiple, delimiter, deprecatedWarning), owner)
diff --git a/endorsedLibraries/kotlinx.cli/src/tests/ArgumentsTests.kt b/endorsedLibraries/kotlinx.cli/src/tests/ArgumentsTests.kt
index 32069536507..db49aa8e2b4 100644
--- a/endorsedLibraries/kotlinx.cli/src/tests/ArgumentsTests.kt
+++ b/endorsedLibraries/kotlinx.cli/src/tests/ArgumentsTests.kt
@@ -26,7 +26,7 @@ class ArgumentsTests {
     fun testArgumetsWithAnyNumberOfValues() {
         val argParser = ArgParser("testParser")
         val output by argParser.argument(ArgType.String, "output", "Output file")
-        val inputs by argParser.argument(ArgType.String, description = "Input files").number()
+        val inputs by argParser.argument(ArgType.String, description = "Input files").vararg()
         argParser.parse(arrayOf("out.txt", "input1.txt", "input2.txt", "input3.txt",
                 "input4.txt"))
         assertEquals("out.txt", output)
@@ -36,7 +36,7 @@ class ArgumentsTests {
     @Test
     fun testArgumetsWithSeveralValues() {
         val argParser = ArgParser("testParser")
-        val addendums by argParser.argument(ArgType.Int, "addendums", description = "Addendums").number(2)
+        val addendums by argParser.argument(ArgType.Int, "addendums", description = "Addendums").multiple(2)
         val output by argParser.argument(ArgType.String, "output", "Output file")
         val debugMode by argParser.option(ArgType.Boolean, "debug", "d", "Debug mode")
         argParser.parse(arrayOf("2", "-d", "3", "out.txt"))
@@ -50,7 +50,7 @@ class ArgumentsTests {
     @Test
     fun testSkippingExtraArguments() {
         val argParser = ArgParser("testParser", skipExtraArguments = true)
-        val addendums by argParser.argument(ArgType.Int, "addendums", description = "Addendums").number(2)
+        val addendums by argParser.argument(ArgType.Int, "addendums", description = "Addendums").multiple(2)
         val output by argParser.argument(ArgType.String, "output", "Output file")
         val debugMode by argParser.option(ArgType.Boolean, "debug", "d", "Debug mode")
         argParser.parse(arrayOf("2", "-d", "3", "out.txt", "something", "else", "in", "string"))
diff --git a/endorsedLibraries/kotlinx.cli/src/tests/ErrorTests.kt b/endorsedLibraries/kotlinx.cli/src/tests/ErrorTests.kt
index 8e53ee35718..411d3f48738 100644
--- a/endorsedLibraries/kotlinx.cli/src/tests/ErrorTests.kt
+++ b/endorsedLibraries/kotlinx.cli/src/tests/ErrorTests.kt
@@ -13,7 +13,7 @@ class ErrorTests {
     @Test
     fun testExtraArguments() {
         val argParser = ArgParser("testParser")
-        val addendums by argParser.argument(ArgType.Int, "addendums", description = "Addendums").number(2)
+        val addendums by argParser.argument(ArgType.Int, "addendums", description = "Addendums").multiple(2)
         val output by argParser.argument(ArgType.String, "output", "Output file")
         val debugMode by argParser.option(ArgType.Boolean, "debug", "d", "Debug mode")
         val exception = assertFailsWith<IllegalStateException> { argParser.parse(
diff --git a/endorsedLibraries/kotlinx.cli/src/tests/SubcommandsTests.kt b/endorsedLibraries/kotlinx.cli/src/tests/SubcommandsTests.kt
index 1a8d0e5f89f..acaf848c77a 100644
--- a/endorsedLibraries/kotlinx.cli/src/tests/SubcommandsTests.kt
+++ b/endorsedLibraries/kotlinx.cli/src/tests/SubcommandsTests.kt
@@ -18,7 +18,7 @@ class SubcommandsTests {
         val output by argParser.option(ArgType.String, "output", "o", "Output file")
         class Summary: Subcommand("summary") {
             val invert by option(ArgType.Boolean, "invert", "i", "Invert results")
-            val addendums by argument(ArgType.Int, "addendums", description = "Addendums").number()
+            val addendums by argument(ArgType.Int, "addendums", description = "Addendums").vararg()
             var result: Int = 0
 
             override fun execute() {
@@ -36,7 +36,7 @@ class SubcommandsTests {
     @Test
     fun testCommonOptions() {
         abstract class CommonOptions(name: String): Subcommand(name) {
-            val numbers by argument(ArgType.Int, "numbers", description = "Numbers").number()
+            val numbers by argument(ArgType.Int, "numbers", description = "Numbers").vararg()
         }
         class Summary: CommonOptions("summary") {
             val invert by option(ArgType.Boolean, "invert", "i", "Invert results")
@@ -74,7 +74,7 @@ class SubcommandsTests {
         val argParser = ArgParser("testParser")
 
         class Summary: Subcommand("summary") {
-            val addendums by argument(ArgType.Int, "addendums", description = "Addendums").number()
+            val addendums by argument(ArgType.Int, "addendums", description = "Addendums").vararg()
             var result: Int = 0
 
             override fun execute() {