diff --git a/compiler/testData/diagnostics/tests/builderInference/issues/kt63841.fir.kt b/compiler/testData/diagnostics/tests/builderInference/issues/kt63841.fir.kt
new file mode 100644
index 00000000000..961c038a65a
--- /dev/null
+++ b/compiler/testData/diagnostics/tests/builderInference/issues/kt63841.fir.kt
@@ -0,0 +1,50 @@
+// ISSUE: KT-63841
+// CHECK_TYPE_WITH_EXACT
+
+class TargetType { fun targetTypeMemberFunction() {} }
+class DifferentType
+
+fun test() {
+    val targetTypeBuildee = build {
+        var variable = getTypeVariable()
+        variable = TargetType()
+        variable.targetTypeMemberFunction()
+    }
+    // exact type equality check — turns unexpected compile-time behavior into red code
+    // considered to be non-user-reproducible code for the purposes of these tests
+    checkExactType<Buildee<TargetType>>(targetTypeBuildee)
+
+    val differentTypeBuildee = build {
+        var variable = getTypeVariable()
+        variable = DifferentType()
+        variable.<!UNRESOLVED_REFERENCE!>targetTypeMemberFunction<!>()
+    }
+    // exact type equality check — turns unexpected compile-time behavior into red code
+    // considered to be non-user-reproducible code for the purposes of these tests
+    checkExactType<Buildee<DifferentType>>(differentTypeBuildee)
+
+    val anyBuildee = build {
+        var variable = getTypeVariable()
+        variable = TargetType()
+        variable.targetTypeMemberFunction()
+        variable = DifferentType()
+        variable.<!UNRESOLVED_REFERENCE!>targetTypeMemberFunction<!>()
+        variable = TargetType()
+        variable.targetTypeMemberFunction()
+    }
+    // exact type equality check — turns unexpected compile-time behavior into red code
+    // considered to be non-user-reproducible code for the purposes of these tests
+    checkExactType<Buildee<Any>>(anyBuildee)
+}
+
+
+
+
+class Buildee<TV> {
+    fun getTypeVariable(): TV = storage
+    private var storage: TV = null!!
+}
+
+fun <PTV> build(instructions: Buildee<PTV>.() -> Unit): Buildee<PTV> {
+    return Buildee<PTV>().apply(instructions)
+}
diff --git a/compiler/testData/diagnostics/tests/builderInference/issues/kt63841.kt b/compiler/testData/diagnostics/tests/builderInference/issues/kt63841.kt
new file mode 100644
index 00000000000..824af0d60d5
--- /dev/null
+++ b/compiler/testData/diagnostics/tests/builderInference/issues/kt63841.kt
@@ -0,0 +1,50 @@
+// ISSUE: KT-63841
+// CHECK_TYPE_WITH_EXACT
+
+class TargetType { fun targetTypeMemberFunction() {} }
+class DifferentType
+
+fun test() {
+    val targetTypeBuildee = build {
+        var variable = <!VARIABLE_WITH_REDUNDANT_INITIALIZER!>getTypeVariable()<!>
+        variable = TargetType()
+        variable.targetTypeMemberFunction()
+    }
+    // exact type equality check — turns unexpected compile-time behavior into red code
+    // considered to be non-user-reproducible code for the purposes of these tests
+    checkExactType<Buildee<TargetType>>(<!TYPE_MISMATCH("Buildee<TargetType>; Buildee<TargetType?>"), TYPE_MISMATCH("Buildee<TargetType?>; Buildee<TargetType>")!>targetTypeBuildee<!>)
+
+    val differentTypeBuildee = <!NEW_INFERENCE_NO_INFORMATION_FOR_PARAMETER!>build<!> {
+        var variable = <!VARIABLE_WITH_REDUNDANT_INITIALIZER!>getTypeVariable()<!>
+        variable = DifferentType()
+        variable.<!DEBUG_INFO_ELEMENT_WITH_ERROR_TYPE, DEBUG_INFO_UNRESOLVED_WITH_TARGET, UNRESOLVED_REFERENCE!>targetTypeMemberFunction<!>()
+    }
+    // exact type equality check — turns unexpected compile-time behavior into red code
+    // considered to be non-user-reproducible code for the purposes of these tests
+    checkExactType<Buildee<DifferentType>>(<!DEBUG_INFO_ELEMENT_WITH_ERROR_TYPE!>differentTypeBuildee<!>)
+
+    val anyBuildee = build {
+        var variable = <!VARIABLE_WITH_REDUNDANT_INITIALIZER!>getTypeVariable()<!>
+        variable = TargetType()
+        variable.targetTypeMemberFunction()
+        variable = DifferentType()
+        variable.<!DEBUG_INFO_ELEMENT_WITH_ERROR_TYPE, DEBUG_INFO_UNRESOLVED_WITH_TARGET, UNRESOLVED_REFERENCE!>targetTypeMemberFunction<!>()
+        variable = TargetType()
+        variable.targetTypeMemberFunction()
+    }
+    // exact type equality check — turns unexpected compile-time behavior into red code
+    // considered to be non-user-reproducible code for the purposes of these tests
+    checkExactType<Buildee<Any>>(<!TYPE_MISMATCH("Buildee<Any>; Buildee<TargetType>"), TYPE_MISMATCH("Buildee<TargetType>; Buildee<Any>")!>anyBuildee<!>)
+}
+
+
+
+
+class Buildee<TV> {
+    fun getTypeVariable(): TV = storage
+    private var storage: TV = null!!
+}
+
+fun <PTV> build(instructions: Buildee<PTV>.() -> Unit): Buildee<PTV> {
+    return Buildee<PTV>().apply(instructions)
+}