diff --git a/compiler/fir/fir2ir/src/org/jetbrains/kotlin/fir/backend/Fir2IrTypeConverter.kt b/compiler/fir/fir2ir/src/org/jetbrains/kotlin/fir/backend/Fir2IrTypeConverter.kt
index f0a3579b764..79349cd0bfc 100644
--- a/compiler/fir/fir2ir/src/org/jetbrains/kotlin/fir/backend/Fir2IrTypeConverter.kt
+++ b/compiler/fir/fir2ir/src/org/jetbrains/kotlin/fir/backend/Fir2IrTypeConverter.kt
@@ -363,3 +363,8 @@ context(Fir2IrComponents)
 internal fun ConeKotlinType.approximateForIrOrNull(): ConeKotlinType? {
     return session.typeApproximator.approximateToSuperType(this, TypeApproximatorConfiguration.FrontendToBackendTypesApproximation)
 }
+
+context(Fir2IrComponents)
+internal fun ConeKotlinType.approximateForIrOrSelf(): ConeKotlinType {
+    return approximateForIrOrNull() ?: this
+}
diff --git a/compiler/fir/fir2ir/src/org/jetbrains/kotlin/fir/backend/generators/AdapterGenerator.kt b/compiler/fir/fir2ir/src/org/jetbrains/kotlin/fir/backend/generators/AdapterGenerator.kt
index 1c47bb80ed7..1ed478b8998 100644
--- a/compiler/fir/fir2ir/src/org/jetbrains/kotlin/fir/backend/generators/AdapterGenerator.kt
+++ b/compiler/fir/fir2ir/src/org/jetbrains/kotlin/fir/backend/generators/AdapterGenerator.kt
@@ -426,14 +426,26 @@ internal class AdapterGenerator(
     private fun castArgumentToFunctionalInterfaceForSamType(
         argument: IrExpression,
         argumentConeType: ConeKotlinType,
-        samType: ConeKotlinType
+        samType: ConeKotlinType,
     ): IrExpression {
-        val coneKotlinFunctionType = getFunctionTypeForPossibleSamType(samType) ?: return argument
+        // The rule for SAM conversions is:
+        // the argument must be a non-reflection function type and be a subtype of the required function type.
+        // We handle intersection types, captured types, etc. by approximating both expected and actual types.
+        val approximatedConeKotlinFunctionType = getFunctionTypeForPossibleSamType(samType)?.approximateForIrOrSelf() ?: return argument
+
         // This line is not present in the K1 counterpart because there is InsertImplicitCasts::cast that effectively removes
         // such unnecessary casts. At the same time, many IR lowerings assume that there are no such redundant casts and many
         // tests from FirBlackBoxCodegenTestGenerated relevant to INDY start failing once this line is removed.
-        if (argumentConeType.isSubtypeOf(coneKotlinFunctionType, session)) return argument
-        val irFunctionType = coneKotlinFunctionType.toIrType()
+        val approximateArgumentConeType = argumentConeType.approximateForIrOrSelf()
+
+        if (approximateArgumentConeType.isSubtypeOf(approximatedConeKotlinFunctionType, session)
+        // TODO uncomment when KT-63510 is fixed, probably fixes KT-62865
+        // && approximateArgumentConeType.lowerBoundIfFlexible().functionTypeKind(session)?.isReflectType == false
+        ) {
+            return argument
+        }
+
+        val irFunctionType = approximatedConeKotlinFunctionType.toIrType()
         return argument.implicitCastTo(irFunctionType)
     }
 
diff --git a/compiler/testData/ir/irText/expressions/funInterface/samConversionsWithSmartCasts.fir.ir.txt b/compiler/testData/ir/irText/expressions/funInterface/samConversionsWithSmartCasts.fir.ir.txt
index f6a2af9bdac..3c9aa904cc2 100644
--- a/compiler/testData/ir/irText/expressions/funInterface/samConversionsWithSmartCasts.fir.ir.txt
+++ b/compiler/testData/ir/irText/expressions/funInterface/samConversionsWithSmartCasts.fir.ir.txt
@@ -125,7 +125,8 @@ FILE fqName:<root> fileName:/samConversionsWithSmartCasts.kt
           GET_VAR 'a: kotlin.Function1<kotlin.Int, kotlin.Int> declared in <root>.test7' type=kotlin.Function1<kotlin.Int, kotlin.Int> origin=null
       CALL 'public final fun run1 (r: <root>.KRunnable): kotlin.Unit declared in <root>' type=kotlin.Unit origin=null
         r: TYPE_OP type=<root>.KRunnable origin=SAM_CONVERSION typeOperand=<root>.KRunnable
-          GET_VAR 'a: kotlin.Function1<kotlin.Int, kotlin.Int> declared in <root>.test7' type=kotlin.Function1<kotlin.Int, kotlin.Int> origin=null
+          TYPE_OP type=kotlin.Function0<kotlin.Unit> origin=IMPLICIT_CAST typeOperand=kotlin.Function0<kotlin.Unit>
+            GET_VAR 'a: kotlin.Function1<kotlin.Int, kotlin.Int> declared in <root>.test7' type=kotlin.Function1<kotlin.Int, kotlin.Int> origin=null
   FUN name:test7a visibility:public modality:FINAL <T> (a:T of <root>.test7a) returnType:kotlin.Unit
     TYPE_PARAMETER name:T index:0 variance: superTypes:[kotlin.Function1<kotlin.Int, kotlin.Int>] reified:false
     VALUE_PARAMETER name:a index:0 type:T of <root>.test7a
@@ -135,7 +136,8 @@ FILE fqName:<root> fileName:/samConversionsWithSmartCasts.kt
           GET_VAR 'a: T of <root>.test7a declared in <root>.test7a' type=T of <root>.test7a origin=null
       CALL 'public final fun run1 (r: <root>.KRunnable): kotlin.Unit declared in <root>' type=kotlin.Unit origin=null
         r: TYPE_OP type=<root>.KRunnable origin=SAM_CONVERSION typeOperand=<root>.KRunnable
-          GET_VAR 'a: T of <root>.test7a declared in <root>.test7a' type=T of <root>.test7a origin=null
+          TYPE_OP type=kotlin.Function0<kotlin.Unit> origin=IMPLICIT_CAST typeOperand=kotlin.Function0<kotlin.Unit>
+            GET_VAR 'a: T of <root>.test7a declared in <root>.test7a' type=T of <root>.test7a origin=null
   FUN name:test7b visibility:public modality:FINAL <T> (a:T of <root>.test7b) returnType:kotlin.Unit
     TYPE_PARAMETER name:T index:0 variance: superTypes:[kotlin.Function1<kotlin.Int, kotlin.Unit>; kotlin.Function0<kotlin.Unit>] reified:false
     VALUE_PARAMETER name:a index:0 type:T of <root>.test7b
@@ -178,3 +180,23 @@ FILE fqName:<root> fileName:/samConversionsWithSmartCasts.kt
       CALL 'public final fun run1 (r: <root>.KRunnable): kotlin.Unit declared in <root>' type=kotlin.Unit origin=null
         r: TYPE_OP type=<root>.KRunnable origin=SAM_CONVERSION typeOperand=<root>.KRunnable
           FUNCTION_REFERENCE 'public final fun test9 (): kotlin.Unit declared in <root>' type=kotlin.reflect.KFunction0<kotlin.Unit> origin=null reflectionTarget=<same>
+  FUN name:test10 visibility:public modality:FINAL <> (a:kotlin.Any) returnType:kotlin.Unit
+    VALUE_PARAMETER name:a index:0 type:kotlin.Any
+    BLOCK_BODY
+      WHEN type=kotlin.Unit origin=IF
+        BRANCH
+          if: WHEN type=kotlin.Boolean origin=ANDAND
+            BRANCH
+              if: TYPE_OP type=kotlin.Boolean origin=INSTANCEOF typeOperand=<root>.Unrelated
+                GET_VAR 'a: kotlin.Any declared in <root>.test10' type=kotlin.Any origin=null
+              then: TYPE_OP type=kotlin.Boolean origin=INSTANCEOF typeOperand=kotlin.Function0<kotlin.Unit>
+                TYPE_OP type=<root>.Unrelated origin=IMPLICIT_CAST typeOperand=<root>.Unrelated
+                  GET_VAR 'a: kotlin.Any declared in <root>.test10' type=kotlin.Any origin=null
+            BRANCH
+              if: CONST Boolean type=kotlin.Boolean value=true
+              then: CONST Boolean type=kotlin.Boolean value=false
+          then: BLOCK type=kotlin.Unit origin=null
+            CALL 'public final fun run1 (r: <root>.KRunnable): kotlin.Unit declared in <root>' type=kotlin.Unit origin=null
+              r: TYPE_OP type=<root>.KRunnable origin=SAM_CONVERSION typeOperand=<root>.KRunnable
+                TYPE_OP type=kotlin.Function0<kotlin.Unit> origin=IMPLICIT_CAST typeOperand=kotlin.Function0<kotlin.Unit>
+                  GET_VAR 'a: kotlin.Any declared in <root>.test10' type=kotlin.Any origin=null
diff --git a/compiler/testData/ir/irText/expressions/funInterface/samConversionsWithSmartCasts.fir.kt.txt b/compiler/testData/ir/irText/expressions/funInterface/samConversionsWithSmartCasts.fir.kt.txt
index aa519312dbc..38ce376d9d8 100644
--- a/compiler/testData/ir/irText/expressions/funInterface/samConversionsWithSmartCasts.fir.kt.txt
+++ b/compiler/testData/ir/irText/expressions/funInterface/samConversionsWithSmartCasts.fir.kt.txt
@@ -70,12 +70,12 @@ fun test6(a: Any) {
 
 fun test7(a: Function1<Int, Int>) {
   a as Function0<Unit> /*~> Unit */
-  run1(r = a /*-> KRunnable */)
+  run1(r = a /*as Function0<Unit> */ /*-> KRunnable */)
 }
 
 fun <T : Function1<Int, Int>> test7a(a: T) {
   a as Function0<Unit> /*~> Unit */
-  run1(r = a /*-> KRunnable */)
+  run1(r = a /*as Function0<Unit> */ /*-> KRunnable */)
 }
 
 fun <T> test7b(a: T) where T : Function1<Int, Unit>, T : Function0<Unit> {
@@ -97,3 +97,14 @@ fun test9() {
   run1(r = ::test9 /*-> KRunnable */)
 }
 
+fun test10(a: Any) {
+  when {
+    when {
+      a is Unrelated -> a /*as Unrelated */ is Function0<Unit>
+      else -> false
+    } -> { // BLOCK
+      run1(r = a /*as Function0<Unit> */ /*-> KRunnable */)
+    }
+  }
+}
+
diff --git a/compiler/testData/ir/irText/expressions/funInterface/samConversionsWithSmartCasts.ir.txt b/compiler/testData/ir/irText/expressions/funInterface/samConversionsWithSmartCasts.ir.txt
index 67d646c021a..b49994cf50e 100644
--- a/compiler/testData/ir/irText/expressions/funInterface/samConversionsWithSmartCasts.ir.txt
+++ b/compiler/testData/ir/irText/expressions/funInterface/samConversionsWithSmartCasts.ir.txt
@@ -179,3 +179,22 @@ FILE fqName:<root> fileName:/samConversionsWithSmartCasts.kt
       CALL 'public final fun run1 (r: <root>.KRunnable): kotlin.Unit declared in <root>' type=kotlin.Unit origin=null
         r: TYPE_OP type=<root>.KRunnable origin=SAM_CONVERSION typeOperand=<root>.KRunnable
           FUNCTION_REFERENCE 'public final fun test9 (): kotlin.Unit declared in <root>' type=kotlin.reflect.KFunction0<kotlin.Unit> origin=null reflectionTarget=<same>
+  FUN name:test10 visibility:public modality:FINAL <> (a:kotlin.Any) returnType:kotlin.Unit
+    VALUE_PARAMETER name:a index:0 type:kotlin.Any
+    BLOCK_BODY
+      WHEN type=kotlin.Unit origin=IF
+        BRANCH
+          if: WHEN type=kotlin.Boolean origin=ANDAND
+            BRANCH
+              if: TYPE_OP type=kotlin.Boolean origin=INSTANCEOF typeOperand=<root>.Unrelated
+                GET_VAR 'a: kotlin.Any declared in <root>.test10' type=kotlin.Any origin=null
+              then: TYPE_OP type=kotlin.Boolean origin=INSTANCEOF typeOperand=kotlin.Function0<kotlin.Unit>
+                GET_VAR 'a: kotlin.Any declared in <root>.test10' type=kotlin.Any origin=null
+            BRANCH
+              if: CONST Boolean type=kotlin.Boolean value=true
+              then: CONST Boolean type=kotlin.Boolean value=false
+          then: BLOCK type=kotlin.Unit origin=null
+            CALL 'public final fun run1 (r: <root>.KRunnable): kotlin.Unit declared in <root>' type=kotlin.Unit origin=null
+              r: TYPE_OP type=<root>.KRunnable origin=SAM_CONVERSION typeOperand=<root>.KRunnable
+                TYPE_OP type=kotlin.Function0<kotlin.Unit> origin=IMPLICIT_CAST typeOperand=kotlin.Function0<kotlin.Unit>
+                  GET_VAR 'a: kotlin.Any declared in <root>.test10' type=kotlin.Any origin=null
diff --git a/compiler/testData/ir/irText/expressions/funInterface/samConversionsWithSmartCasts.kt b/compiler/testData/ir/irText/expressions/funInterface/samConversionsWithSmartCasts.kt
index e5e4a65a59d..bf0d5362034 100644
--- a/compiler/testData/ir/irText/expressions/funInterface/samConversionsWithSmartCasts.kt
+++ b/compiler/testData/ir/irText/expressions/funInterface/samConversionsWithSmartCasts.kt
@@ -79,3 +79,11 @@ fun test8(a: () -> Unit) {
 fun test9() {
     run1(::test9)
 }
+
+// KT-63345
+fun test10(a: Any) {
+    @Suppress("CANNOT_CHECK_FOR_ERASED")
+    if (a is Unrelated && a is (() -> Unit)) {
+        run1(a)
+    }
+}
diff --git a/compiler/testData/ir/irText/expressions/funInterface/samConversionsWithSmartCasts.kt.txt b/compiler/testData/ir/irText/expressions/funInterface/samConversionsWithSmartCasts.kt.txt
index 84fbd888a6d..a60696ee3ed 100644
--- a/compiler/testData/ir/irText/expressions/funInterface/samConversionsWithSmartCasts.kt.txt
+++ b/compiler/testData/ir/irText/expressions/funInterface/samConversionsWithSmartCasts.kt.txt
@@ -96,3 +96,14 @@ fun test8(a: Function0<Unit>) {
 fun test9() {
   run1(r = ::test9 /*-> KRunnable */)
 }
+
+fun test10(a: Any) {
+  when {
+    when {
+      a is Unrelated -> a is Function0<Unit>
+      else -> false
+    } -> { // BLOCK
+      run1(r = a /*as Function0<Unit> */ /*-> KRunnable */)
+    }
+  }
+}
diff --git a/compiler/testData/ir/irText/expressions/funInterface/samConversionsWithSmartCasts.sig.kt.txt b/compiler/testData/ir/irText/expressions/funInterface/samConversionsWithSmartCasts.sig.kt.txt
index 817d0a41186..37de316b115 100644
--- a/compiler/testData/ir/irText/expressions/funInterface/samConversionsWithSmartCasts.sig.kt.txt
+++ b/compiler/testData/ir/irText/expressions/funInterface/samConversionsWithSmartCasts.sig.kt.txt
@@ -50,6 +50,12 @@ fun <T> test0(a: T): Unit where T : KRunnable, T : Function0<Unit>
 //   Public signature debug description: test1(kotlin.Function0<kotlin.Unit>){}
 fun test1(a: Function0<Unit>): Unit
 
+// CHECK:
+//   Mangled name: #test10(kotlin.Any){}
+//   Public signature: /test10|8673682583765656768[0]
+//   Public signature debug description: test10(kotlin.Any){}
+fun test10(a: Any): Unit
+
 // CHECK:
 //   Mangled name: #test2(KRunnable){}
 //   Public signature: /test2|-6262171320756539088[0]
diff --git a/compiler/testData/ir/irText/expressions/sam/samConversionsWithSmartCasts.fir.ir.txt b/compiler/testData/ir/irText/expressions/sam/samConversionsWithSmartCasts.fir.ir.txt
index a842958304f..544bfee590c 100644
--- a/compiler/testData/ir/irText/expressions/sam/samConversionsWithSmartCasts.fir.ir.txt
+++ b/compiler/testData/ir/irText/expressions/sam/samConversionsWithSmartCasts.fir.ir.txt
@@ -99,7 +99,8 @@ FILE fqName:<root> fileName:/samConversionsWithSmartCasts.kt
       CALL 'public open fun run1 (r: @[FlexibleNullability] java.lang.Runnable?): kotlin.Unit declared in <root>.J' type=kotlin.Unit origin=null
         $this: CONSTRUCTOR_CALL 'public constructor <init> () declared in <root>.J' type=<root>.J origin=null
         r: TYPE_OP type=java.lang.Runnable origin=SAM_CONVERSION typeOperand=java.lang.Runnable
-          GET_VAR 'a: kotlin.Function1<kotlin.Int, kotlin.Int> declared in <root>.test7' type=kotlin.Function1<kotlin.Int, kotlin.Int> origin=null
+          TYPE_OP type=kotlin.Function0<kotlin.Unit> origin=IMPLICIT_CAST typeOperand=kotlin.Function0<kotlin.Unit>
+            GET_VAR 'a: kotlin.Function1<kotlin.Int, kotlin.Int> declared in <root>.test7' type=kotlin.Function1<kotlin.Int, kotlin.Int> origin=null
   FUN name:test8 visibility:public modality:FINAL <> (a:kotlin.Function0<kotlin.Unit>) returnType:kotlin.Unit
     VALUE_PARAMETER name:a index:0 type:kotlin.Function0<kotlin.Unit>
     BLOCK_BODY
diff --git a/compiler/testData/ir/irText/expressions/sam/samConversionsWithSmartCasts.fir.kt.txt b/compiler/testData/ir/irText/expressions/sam/samConversionsWithSmartCasts.fir.kt.txt
index 01ff674e970..fcd384296f9 100644
--- a/compiler/testData/ir/irText/expressions/sam/samConversionsWithSmartCasts.fir.kt.txt
+++ b/compiler/testData/ir/irText/expressions/sam/samConversionsWithSmartCasts.fir.kt.txt
@@ -54,7 +54,7 @@ fun test6(a: Any) {
 
 fun test7(a: Function1<Int, Int>) {
   a as Function0<Unit> /*~> Unit */
-  J().run1(r = a /*-> Runnable */)
+  J().run1(r = a /*as Function0<Unit> */ /*-> Runnable */)
 }
 
 fun test8(a: Function0<Unit>) {