diff --git a/analysis/low-level-api-fir/tests/org/jetbrains/kotlin/analysis/low/level/api/fir/diagnostic/compiler/based/DiagnosisCompilerFirTestdataTestGenerated.java b/analysis/low-level-api-fir/tests/org/jetbrains/kotlin/analysis/low/level/api/fir/diagnostic/compiler/based/DiagnosisCompilerFirTestdataTestGenerated.java
index ca7ef011213..88c166100b9 100644
--- a/analysis/low-level-api-fir/tests/org/jetbrains/kotlin/analysis/low/level/api/fir/diagnostic/compiler/based/DiagnosisCompilerFirTestdataTestGenerated.java
+++ b/analysis/low-level-api-fir/tests/org/jetbrains/kotlin/analysis/low/level/api/fir/diagnostic/compiler/based/DiagnosisCompilerFirTestdataTestGenerated.java
@@ -1212,6 +1212,12 @@ public class DiagnosisCompilerFirTestdataTestGenerated extends AbstractDiagnosis
             public void testReassignOfNonMemberProperty_lateInitialization() throws Exception {
                 runTest("compiler/fir/analysis-tests/testData/resolve/cfa/reassignOfNonMemberProperty_lateInitialization.kt");
             }
+
+            @Test
+            @TestMetadata("smartcastOnThisDuringClassInitialization.kt")
+            public void testSmartcastOnThisDuringClassInitialization() throws Exception {
+                runTest("compiler/fir/analysis-tests/testData/resolve/cfa/smartcastOnThisDuringClassInitialization.kt");
+            }
         }
 
         @Nested
diff --git a/compiler/fir/analysis-tests/legacy-fir-tests/tests-gen/org/jetbrains/kotlin/fir/LazyBodyIsNotTouchedTilContractsPhaseTestGenerated.java b/compiler/fir/analysis-tests/legacy-fir-tests/tests-gen/org/jetbrains/kotlin/fir/LazyBodyIsNotTouchedTilContractsPhaseTestGenerated.java
index a3d5fdf5de6..07cbd6bc388 100644
--- a/compiler/fir/analysis-tests/legacy-fir-tests/tests-gen/org/jetbrains/kotlin/fir/LazyBodyIsNotTouchedTilContractsPhaseTestGenerated.java
+++ b/compiler/fir/analysis-tests/legacy-fir-tests/tests-gen/org/jetbrains/kotlin/fir/LazyBodyIsNotTouchedTilContractsPhaseTestGenerated.java
@@ -1045,6 +1045,11 @@ public class LazyBodyIsNotTouchedTilContractsPhaseTestGenerated extends Abstract
         public void testReassignOfNonMemberProperty_lateInitialization() throws Exception {
             runTest("compiler/fir/analysis-tests/testData/resolve/cfa/reassignOfNonMemberProperty_lateInitialization.kt");
         }
+
+        @TestMetadata("smartcastOnThisDuringClassInitialization.kt")
+        public void testSmartcastOnThisDuringClassInitialization() throws Exception {
+            runTest("compiler/fir/analysis-tests/testData/resolve/cfa/smartcastOnThisDuringClassInitialization.kt");
+        }
     }
 
     @TestMetadata("compiler/fir/analysis-tests/testData/resolve/cfg")
diff --git a/compiler/fir/analysis-tests/testData/resolve/cfa/smartcastOnThisDuringClassInitialization.fir.txt b/compiler/fir/analysis-tests/testData/resolve/cfa/smartcastOnThisDuringClassInitialization.fir.txt
new file mode 100644
index 00000000000..036904a75ba
--- /dev/null
+++ b/compiler/fir/analysis-tests/testData/resolve/cfa/smartcastOnThisDuringClassInitialization.fir.txt
@@ -0,0 +1,17 @@
+FILE: smartcastOnThisDuringClassInitialization.kt
+    public abstract interface I : R|kotlin/Any| {
+    }
+    public open class Some : R|kotlin/Any| {
+        public constructor(): R|Some| {
+            super<R|kotlin/Any|>()
+        }
+
+        public final val x: R|kotlin/Int|
+            public get(): R|kotlin/Int|
+
+        init {
+            (this@R|/Some| as R|I|)
+            this@R|/Some|.R|/Some.x| = Int(1)
+        }
+
+    }
diff --git a/compiler/fir/analysis-tests/testData/resolve/cfa/smartcastOnThisDuringClassInitialization.kt b/compiler/fir/analysis-tests/testData/resolve/cfa/smartcastOnThisDuringClassInitialization.kt
new file mode 100644
index 00000000000..d450c98948a
--- /dev/null
+++ b/compiler/fir/analysis-tests/testData/resolve/cfa/smartcastOnThisDuringClassInitialization.kt
@@ -0,0 +1,11 @@
+// ISSUE: KT-56863
+interface I
+
+open class Some {
+    val x: Int
+
+    init {
+        this as I
+        x = 1
+    }
+}
diff --git a/compiler/fir/analysis-tests/tests-gen/org/jetbrains/kotlin/test/runners/FirLightTreeDiagnosticsTestGenerated.java b/compiler/fir/analysis-tests/tests-gen/org/jetbrains/kotlin/test/runners/FirLightTreeDiagnosticsTestGenerated.java
index 3e8a9fbf2f9..70589815801 100644
--- a/compiler/fir/analysis-tests/tests-gen/org/jetbrains/kotlin/test/runners/FirLightTreeDiagnosticsTestGenerated.java
+++ b/compiler/fir/analysis-tests/tests-gen/org/jetbrains/kotlin/test/runners/FirLightTreeDiagnosticsTestGenerated.java
@@ -1212,6 +1212,12 @@ public class FirLightTreeDiagnosticsTestGenerated extends AbstractFirLightTreeDi
             public void testReassignOfNonMemberProperty_lateInitialization() throws Exception {
                 runTest("compiler/fir/analysis-tests/testData/resolve/cfa/reassignOfNonMemberProperty_lateInitialization.kt");
             }
+
+            @Test
+            @TestMetadata("smartcastOnThisDuringClassInitialization.kt")
+            public void testSmartcastOnThisDuringClassInitialization() throws Exception {
+                runTest("compiler/fir/analysis-tests/testData/resolve/cfa/smartcastOnThisDuringClassInitialization.kt");
+            }
         }
 
         @Nested
diff --git a/compiler/fir/analysis-tests/tests-gen/org/jetbrains/kotlin/test/runners/FirPsiDiagnosticTestGenerated.java b/compiler/fir/analysis-tests/tests-gen/org/jetbrains/kotlin/test/runners/FirPsiDiagnosticTestGenerated.java
index a89d87300ad..fe5a1a02bdb 100644
--- a/compiler/fir/analysis-tests/tests-gen/org/jetbrains/kotlin/test/runners/FirPsiDiagnosticTestGenerated.java
+++ b/compiler/fir/analysis-tests/tests-gen/org/jetbrains/kotlin/test/runners/FirPsiDiagnosticTestGenerated.java
@@ -1212,6 +1212,12 @@ public class FirPsiDiagnosticTestGenerated extends AbstractFirPsiDiagnosticTest
             public void testReassignOfNonMemberProperty_lateInitialization() throws Exception {
                 runTest("compiler/fir/analysis-tests/testData/resolve/cfa/reassignOfNonMemberProperty_lateInitialization.kt");
             }
+
+            @Test
+            @TestMetadata("smartcastOnThisDuringClassInitialization.kt")
+            public void testSmartcastOnThisDuringClassInitialization() throws Exception {
+                runTest("compiler/fir/analysis-tests/testData/resolve/cfa/smartcastOnThisDuringClassInitialization.kt");
+            }
         }
 
         @Nested
diff --git a/compiler/fir/checkers/src/org/jetbrains/kotlin/fir/analysis/cfa/FirPropertyInitializationAnalyzer.kt b/compiler/fir/checkers/src/org/jetbrains/kotlin/fir/analysis/cfa/FirPropertyInitializationAnalyzer.kt
index 3f032cb2f6d..0e4beee8529 100644
--- a/compiler/fir/checkers/src/org/jetbrains/kotlin/fir/analysis/cfa/FirPropertyInitializationAnalyzer.kt
+++ b/compiler/fir/checkers/src/org/jetbrains/kotlin/fir/analysis/cfa/FirPropertyInitializationAnalyzer.kt
@@ -18,10 +18,7 @@ import org.jetbrains.kotlin.fir.declarations.*
 import org.jetbrains.kotlin.fir.declarations.utils.hasBackingField
 import org.jetbrains.kotlin.fir.declarations.utils.hasExplicitBackingField
 import org.jetbrains.kotlin.fir.declarations.utils.isLateInit
-import org.jetbrains.kotlin.fir.expressions.FirQualifiedAccessExpression
-import org.jetbrains.kotlin.fir.expressions.FirThisReceiverExpression
-import org.jetbrains.kotlin.fir.expressions.calleeReference
-import org.jetbrains.kotlin.fir.expressions.unwrapLValue
+import org.jetbrains.kotlin.fir.expressions.*
 import org.jetbrains.kotlin.fir.isCatchParameter
 import org.jetbrains.kotlin.fir.references.toResolvedPropertySymbol
 import org.jetbrains.kotlin.fir.resolve.dfa.cfg.*
@@ -95,7 +92,7 @@ private fun PropertyInitializationInfoData.checkPropertyAccesses(
     scopes: MutableMap<FirPropertySymbol, FirDeclaration?>
 ) {
     fun FirQualifiedAccessExpression.hasCorrectReceiver() =
-        (dispatchReceiver as? FirThisReceiverExpression)?.calleeReference?.boundSymbol == receiver
+        (dispatchReceiver.unwrapSmartcastExpression() as? FirThisReceiverExpression)?.calleeReference?.boundSymbol == receiver
 
     for (node in graph.nodes) {
         when {
diff --git a/compiler/fir/checkers/src/org/jetbrains/kotlin/fir/analysis/cfa/util/PropertyInitializationInfoCollector.kt b/compiler/fir/checkers/src/org/jetbrains/kotlin/fir/analysis/cfa/util/PropertyInitializationInfoCollector.kt
index 82936c77fd8..7bf575e52bc 100644
--- a/compiler/fir/checkers/src/org/jetbrains/kotlin/fir/analysis/cfa/util/PropertyInitializationInfoCollector.kt
+++ b/compiler/fir/checkers/src/org/jetbrains/kotlin/fir/analysis/cfa/util/PropertyInitializationInfoCollector.kt
@@ -10,6 +10,7 @@ import org.jetbrains.kotlin.contracts.description.EventOccurrencesRange
 import org.jetbrains.kotlin.fir.expressions.FirThisReceiverExpression
 import org.jetbrains.kotlin.fir.expressions.calleeReference
 import org.jetbrains.kotlin.fir.expressions.dispatchReceiver
+import org.jetbrains.kotlin.fir.expressions.unwrapSmartcastExpression
 import org.jetbrains.kotlin.fir.references.toResolvedPropertySymbol
 import org.jetbrains.kotlin.fir.resolve.dfa.cfg.*
 import org.jetbrains.kotlin.fir.symbols.FirBasedSymbol
@@ -51,7 +52,7 @@ class PropertyInitializationInfoCollector(
         data: PathAwarePropertyInitializationInfo
     ): PathAwarePropertyInitializationInfo {
         val dataForNode = visitNode(node, data)
-        val receiver = (node.fir.dispatchReceiver as? FirThisReceiverExpression)?.calleeReference?.boundSymbol
+        val receiver = (node.fir.dispatchReceiver.unwrapSmartcastExpression() as? FirThisReceiverExpression)?.calleeReference?.boundSymbol
         if (receiver != expectedReceiver) return dataForNode
         val symbol = node.fir.calleeReference?.toResolvedPropertySymbol() ?: return dataForNode
         if (symbol !in localProperties) return dataForNode
diff --git a/compiler/fir/checkers/src/org/jetbrains/kotlin/fir/analysis/checkers/expression/FirReassignmentAndInvisibleSetterChecker.kt b/compiler/fir/checkers/src/org/jetbrains/kotlin/fir/analysis/checkers/expression/FirReassignmentAndInvisibleSetterChecker.kt
index efb2f2942e0..2267359dbf7 100644
--- a/compiler/fir/checkers/src/org/jetbrains/kotlin/fir/analysis/checkers/expression/FirReassignmentAndInvisibleSetterChecker.kt
+++ b/compiler/fir/checkers/src/org/jetbrains/kotlin/fir/analysis/checkers/expression/FirReassignmentAndInvisibleSetterChecker.kt
@@ -139,7 +139,10 @@ object FirReassignmentAndInvisibleSetterChecker : FirVariableAssignmentChecker()
         // Assignments of uninitialized `val`s must be checked via CFG, since the first one is OK.
         // See `FirPropertyInitializationAnalyzer` for locals and `FirMemberPropertiesChecker` for backing fields in initializers.
         if (property.isLocal && property.requiresInitialization(isForClassInitialization = false)) return
-        if (isInOwnersInitializer(expression.dispatchReceiver, context) && property.requiresInitialization(isForClassInitialization = true)) return
+        if (
+            isInOwnersInitializer(expression.dispatchReceiver.unwrapSmartcastExpression(), context)
+            && property.requiresInitialization(isForClassInitialization = true)
+        ) return
 
         reporter.reportOn(expression.lValue.source, FirErrors.VAL_REASSIGNMENT, property, context)
     }