diff --git a/compiler/ir/ir.tree/gen/org/jetbrains/kotlin/ir/util/DeepCopyIrTreeWithSymbols.kt b/compiler/ir/ir.tree/gen/org/jetbrains/kotlin/ir/util/DeepCopyIrTreeWithSymbols.kt
index e69f41f..f248c4d 100644
--- a/compiler/ir/ir.tree/gen/org/jetbrains/kotlin/ir/util/DeepCopyIrTreeWithSymbols.kt
+++ b/compiler/ir/ir.tree/gen/org/jetbrains/kotlin/ir/util/DeepCopyIrTreeWithSymbols.kt
@@ -62,7 +62,7 @@
             with(factory) { declarationCreated() }
             annotations = declaration.annotations.memoryOptimizedMap { it.transform() }
             defaultValue = declaration.defaultValue?.transform()
-            _kind = declaration._kind
+            kind = declaration.kind
             processAttributes(declaration)
         }
 
diff --git a/compiler/ir/ir.tree/src/org/jetbrains/kotlin/ir/builders/declarations/IrValueParameterBuilder.kt b/compiler/ir/ir.tree/src/org/jetbrains/kotlin/ir/builders/declarations/IrValueParameterBuilder.kt
index 36d3f43..a359011 100644
--- a/compiler/ir/ir.tree/src/org/jetbrains/kotlin/ir/builders/declarations/IrValueParameterBuilder.kt
+++ b/compiler/ir/ir.tree/src/org/jetbrains/kotlin/ir/builders/declarations/IrValueParameterBuilder.kt
@@ -12,7 +12,7 @@
 const val UNDEFINED_PARAMETER_INDEX = -1
 
 class IrValueParameterBuilder : IrDeclarationBuilder() {
-    var kind: IrParameterKind? = null
+    var kind: IrParameterKind = IrParameterKind.Regular
     lateinit var type: IrType
 
     var varargElementType: IrType? = null
@@ -24,9 +24,7 @@
     fun updateFrom(from: IrValueParameter) {
         super.updateFrom(from)
 
-        if (from._kind != null) {
-            kind = from._kind
-        }
+        kind = from.kind
         type = from.type
         varargElementType = from.varargElementType
         isCrossInline = from.isCrossinline
diff --git a/compiler/ir/ir.tree/src/org/jetbrains/kotlin/ir/declarations/IrFactory.kt b/compiler/ir/ir.tree/src/org/jetbrains/kotlin/ir/declarations/IrFactory.kt
index bdd7790..1169735 100644
--- a/compiler/ir/ir.tree/src/org/jetbrains/kotlin/ir/declarations/IrFactory.kt
+++ b/compiler/ir/ir.tree/src/org/jetbrains/kotlin/ir/declarations/IrFactory.kt
@@ -415,7 +415,7 @@
         startOffset: Int,
         endOffset: Int,
         origin: IrDeclarationOrigin,
-        kind: IrParameterKind?,
+        kind: IrParameterKind,
         name: Name,
         type: IrType,
         isAssignable: Boolean,
@@ -439,7 +439,7 @@
             isAssignable = isAssignable,
             factory = this
         ).apply {
-            _kind = kind
+            this.kind = kind
         }.declarationCreated()
 
     /**
diff --git a/compiler/ir/ir.tree/src/org/jetbrains/kotlin/ir/declarations/IrFunction.kt b/compiler/ir/ir.tree/src/org/jetbrains/kotlin/ir/declarations/IrFunction.kt
index 4bed052..4a9285a 100644
--- a/compiler/ir/ir.tree/src/org/jetbrains/kotlin/ir/declarations/IrFunction.kt
+++ b/compiler/ir/ir.tree/src/org/jetbrains/kotlin/ir/declarations/IrFunction.kt
@@ -60,16 +60,14 @@
             var newContextParametersCount = 0
             var oldIndex = 0
             for ((index, parameter) in newParameters.withIndex()) {
-                val kind = requireNotNull(parameter._kind) { "Kind must be set explicitly when adding a parameter" }
-
                 parameter.indexInParameters = index
                 @OptIn(DeprecatedForRemovalCompilerApi::class)
-                parameter.indexInOldValueParameters = when (kind) {
+                parameter.indexInOldValueParameters = when (parameter.kind) {
                     IrParameterKind.DispatchReceiver, IrParameterKind.ExtensionReceiver -> -1
                     IrParameterKind.Context, IrParameterKind.Regular -> oldIndex++
                 }
 
-                if (kind == IrParameterKind.Context) {
+                if (parameter.kind == IrParameterKind.Context) {
                     newContextParametersCount++
                 }
             }
@@ -124,7 +122,7 @@
             @OptIn(DeprecatedForRemovalCompilerApi::class)
             old.indexInOldValueParameters = -1
             old.indexInParameters = -1
-            old._kind = null
+            old.kind = IrParameterKind.Regular
 
             if (value != null) {
                 parameters[index] = value
@@ -211,7 +209,7 @@
 
         if (newValueParameters != null) {
             for (param in newValueParameters) {
-                if (param._kind.let { it == IrParameterKind.DispatchReceiver || it == IrParameterKind.ExtensionReceiver }) {
+                if (param.kind.let { it == IrParameterKind.DispatchReceiver || it == IrParameterKind.ExtensionReceiver }) {
                     if (param === parameters.getOrNull(param.indexInParameters)) {
                         throw IllegalArgumentException(
                             "Adding a value parameter ${param.render()} to function ${this.render()}, when it's already present as a receiver.\n" +
@@ -237,7 +235,7 @@
                     param.indexInParameters = -1
                     @OptIn(DeprecatedForRemovalCompilerApi::class)
                     param.indexInOldValueParameters = -1
-                    param._kind = null
+                    param.kind = IrParameterKind.Regular
                 }
             }
         }
@@ -273,8 +271,7 @@
         var indexInOldValueParameters = 0
         for (param in _parameters) {
             @OptIn(DeprecatedForRemovalCompilerApi::class)
-            param.indexInOldValueParameters = when (param._kind) {
-                null -> -1
+            param.indexInOldValueParameters = when (param.kind) {
                 IrParameterKind.DispatchReceiver, IrParameterKind.ExtensionReceiver -> -1
                 IrParameterKind.Context, IrParameterKind.Regular -> indexInOldValueParameters++
             }
diff --git a/compiler/ir/ir.tree/src/org/jetbrains/kotlin/ir/declarations/IrValueParameter.kt b/compiler/ir/ir.tree/src/org/jetbrains/kotlin/ir/declarations/IrValueParameter.kt
index 9176d69..93c100e 100644
--- a/compiler/ir/ir.tree/src/org/jetbrains/kotlin/ir/declarations/IrValueParameter.kt
+++ b/compiler/ir/ir.tree/src/org/jetbrains/kotlin/ir/declarations/IrValueParameter.kt
@@ -70,17 +70,12 @@
         @DelicateIrParameterIndexSetter
         set
 
-    // When using old parameter API, kind is assigned automatically when adding a parameter
-    // to a function. However, up until that moment it is `null`.
-    // When using new API (IrFunction.parameters), `kind` must be set explicitly before adding
-    // a parameter to a function, such as by filling IrFactory.createValueParameter(kind = ...).
-    // It is expected that after migration, all parameters will have a proper kind set upon creation,
-    // and the nullable `_kind` will be dropped.
-    // Before that happens, please use `_kind` in lower level code, that might see a not-yet-attached parameter,
-    // and non-nullable `kind` otherwise, which e.g. enables exhaustive when.
-    internal var _kind: IrParameterKind? = null
+    // Here the kind defaults to Regular, however, unless using the old parameter API,
+    // it is reassigned right away to the specified value (see IrFactory.createValueParameter).
+    // Also, when using the old API, kind is assigned automatically when a parameter is added to a function, and reverts to Regular when removed.
+    var kind: IrParameterKind = IrParameterKind.Regular
         set(value) {
-            if (field === value) return
+            if (field == value) return
             field = value
 
             // When a parameter is already in a function, changing its kind e.g. from regular parameter to
@@ -89,11 +84,6 @@
             // This only affects old-API index, new API is alright.
             (_parent as? IrFunction)?.reindexValueParameters()
         }
-    var kind: IrParameterKind
-        get() = _kind!!
-        set(value) {
-            _kind = value
-        }
 
     abstract var varargElementType: IrType?
 
diff --git a/compiler/ir/ir.tree/src/org/jetbrains/kotlin/ir/util/IrUtils.kt b/compiler/ir/ir.tree/src/org/jetbrains/kotlin/ir/util/IrUtils.kt
index 9c4f000..6a2d03c 100644
--- a/compiler/ir/ir.tree/src/org/jetbrains/kotlin/ir/util/IrUtils.kt
+++ b/compiler/ir/ir.tree/src/org/jetbrains/kotlin/ir/util/IrUtils.kt
@@ -796,7 +796,7 @@
     isCrossinline: Boolean = this.isCrossinline,
     isNoinline: Boolean = this.isNoinline,
     isAssignable: Boolean = this.isAssignable,
-    kind: IrParameterKind? = this._kind,
+    kind: IrParameterKind = this.kind,
 ): IrValueParameter {
     val symbol = IrValueParameterSymbolImpl()
     val defaultValueCopy = defaultValue?.let { originalDefault ->
@@ -811,6 +811,7 @@
         startOffset = startOffset,
         endOffset = endOffset,
         origin = origin,
+        kind = kind,
         name = name,
         type = type,
         isAssignable = isAssignable,
@@ -820,7 +821,6 @@
         isNoinline = isNoinline,
         isHidden = false,
     ).also {
-        it._kind = kind
         it.parent = irFunction
         it.defaultValue = defaultValueCopy
         it.copyAnnotationsFrom(this)
diff --git a/compiler/ir/ir.tree/tree-generator/src/org/jetbrains/kotlin/ir/generator/print/DeepCopyIrTreeWithSymbolsPrinter.kt b/compiler/ir/ir.tree/tree-generator/src/org/jetbrains/kotlin/ir/generator/print/DeepCopyIrTreeWithSymbolsPrinter.kt
index 608142b..5731244 100644
--- a/compiler/ir/ir.tree/tree-generator/src/org/jetbrains/kotlin/ir/generator/print/DeepCopyIrTreeWithSymbolsPrinter.kt
+++ b/compiler/ir/ir.tree/tree-generator/src/org/jetbrains/kotlin/ir/generator/print/DeepCopyIrTreeWithSymbolsPrinter.kt
@@ -222,7 +222,7 @@
                 println("parameters = ${element.visitorParameterName}.parameters.memoryOptimizedMap { it.transform() }")
             }
             if (element.isSubclassOf(IrTree.valueParameter)) {
-                println("_kind = ${element.visitorParameterName}._kind")
+                println("kind = ${element.visitorParameterName}.kind")
             }
             if (element.isSubclassOf(IrTree.file)) {
                 println("module = transformedModule ?: ${element.visitorParameterName}.module")