diff --git a/compiler/fir/fir2ir/tests-gen/org/jetbrains/kotlin/test/runners/codegen/FirBlackBoxCodegenTestGenerated.java b/compiler/fir/fir2ir/tests-gen/org/jetbrains/kotlin/test/runners/codegen/FirBlackBoxCodegenTestGenerated.java
index 9dc0d05f4fe..d62df9234e5 100644
--- a/compiler/fir/fir2ir/tests-gen/org/jetbrains/kotlin/test/runners/codegen/FirBlackBoxCodegenTestGenerated.java
+++ b/compiler/fir/fir2ir/tests-gen/org/jetbrains/kotlin/test/runners/codegen/FirBlackBoxCodegenTestGenerated.java
@@ -46523,6 +46523,12 @@ public class FirBlackBoxCodegenTestGenerated extends AbstractFirBlackBoxCodegenT
             runTest("compiler/testData/codegen/box/sam/kt52417.kt");
         }
 
+        @Test
+        @TestMetadata("kt54600.kt")
+        public void testKt54600() throws Exception {
+            runTest("compiler/testData/codegen/box/sam/kt54600.kt");
+        }
+
         @Test
         @TestMetadata("nonInlinedSamWrapper.kt")
         public void testNonInlinedSamWrapper() throws Exception {
diff --git a/compiler/ir/ir.psi2ir/src/org/jetbrains/kotlin/psi2ir/generators/samConversions.kt b/compiler/ir/ir.psi2ir/src/org/jetbrains/kotlin/psi2ir/generators/samConversions.kt
index 3bb691075ac..657b5349fc0 100644
--- a/compiler/ir/ir.psi2ir/src/org/jetbrains/kotlin/psi2ir/generators/samConversions.kt
+++ b/compiler/ir/ir.psi2ir/src/org/jetbrains/kotlin/psi2ir/generators/samConversions.kt
@@ -13,9 +13,7 @@ import org.jetbrains.kotlin.descriptors.synthetic.FunctionInterfaceAdapterExtens
 import org.jetbrains.kotlin.descriptors.synthetic.FunctionInterfaceConstructorDescriptor
 import org.jetbrains.kotlin.resolve.sam.getFunctionTypeForAbstractMethod
 import org.jetbrains.kotlin.resolve.sam.getSingleAbstractMethodOrNull
-import org.jetbrains.kotlin.types.KotlinType
-import org.jetbrains.kotlin.types.TypeSubstitutor
-import org.jetbrains.kotlin.types.Variance
+import org.jetbrains.kotlin.types.*
 
 fun GeneratorExtensions.SamConversion.isSamType(kotlinType: KotlinType): Boolean {
     val descriptor = kotlinType.constructor.declarationDescriptor
@@ -35,12 +33,23 @@ fun CallableDescriptor.getOriginalForFunctionInterfaceAdapter() =
             null
     }
 
-fun KotlinType.getSubstitutedFunctionTypeForSamType(): KotlinType {
+fun KotlinType.getSubstitutedFunctionTypeForSamType(): KotlinType =
+    when (val unwrapped = this.unwrap()) {
+        is SimpleType -> unwrapped.getSubstitutedFunctionTypeForSamType()
+        is FlexibleType -> KotlinTypeFactory.flexibleType(
+            unwrapped.lowerBound.getSubstitutedFunctionTypeForSamType(),
+            unwrapped.upperBound.getSubstitutedFunctionTypeForSamType(),
+        )
+    }
+
+private fun SimpleType.getSubstitutedFunctionTypeForSamType(): SimpleType {
     val descriptor = constructor.declarationDescriptor as? ClassDescriptor
         ?: throw AssertionError("SAM should be represented by a class: $this")
     val singleAbstractMethod = getSingleAbstractMethodOrNull(descriptor)
         ?: throw AssertionError("$descriptor should have a single abstract method")
-    val unsubstitutedFunctionType = getFunctionTypeForAbstractMethod(singleAbstractMethod, false)
-    return TypeSubstitutor.create(this).substitute(unsubstitutedFunctionType, Variance.INVARIANT)
+    val unsubstitutedFunctionType = getFunctionTypeForAbstractMethod(singleAbstractMethod, false).makeNullableAsSpecified(isMarkedNullable)
+    val result = TypeSubstitutor.create(this).substitute(unsubstitutedFunctionType, Variance.INVARIANT)
         ?: throw AssertionError("Failed to substitute function type $unsubstitutedFunctionType corresponding to $this")
+    return result as? SimpleType
+        ?: throw AssertionError("SAM type substitution result is not a simple type: $this -> $result")
 }
diff --git a/compiler/testData/codegen/box/sam/kt54600.fir.ir.txt b/compiler/testData/codegen/box/sam/kt54600.fir.ir.txt
new file mode 100644
index 00000000000..d01302d38b1
--- /dev/null
+++ b/compiler/testData/codegen/box/sam/kt54600.fir.ir.txt
@@ -0,0 +1,15 @@
+FILE fqName:<root> fileName:/box.kt
+  FUN name:box visibility:public modality:FINAL <> () returnType:kotlin.String
+    BLOCK_BODY
+      RETURN type=kotlin.Nothing from='public final fun box (): kotlin.String declared in <root>'
+        CALL 'public final fun foo (filter: kotlin.Function1<kotlin.String, kotlin.Boolean>?): kotlin.String declared in <root>' type=kotlin.String origin=null
+          filter: CONST Null type=kotlin.Nothing? value=null
+  FUN name:foo visibility:public modality:FINAL <> (filter:kotlin.Function1<kotlin.String, kotlin.Boolean>?) returnType:kotlin.String
+    VALUE_PARAMETER name:filter index:0 type:kotlin.Function1<kotlin.String, kotlin.Boolean>?
+    BLOCK_BODY
+      TYPE_OP type=kotlin.Unit origin=IMPLICIT_COERCION_TO_UNIT typeOperand=kotlin.Unit
+        CONSTRUCTOR_CALL 'public constructor <init> (filter: @[FlexibleNullability] <root>.Condition<in @[FlexibleNullability] kotlin.String?>?) declared in <root>.J' type=<root>.J origin=null
+          filter: TYPE_OP type=@[FlexibleNullability] <root>.Condition<@[FlexibleNullability] kotlin.String?>? origin=SAM_CONVERSION typeOperand=@[FlexibleNullability] <root>.Condition<@[FlexibleNullability] kotlin.String?>?
+            GET_VAR 'filter: kotlin.Function1<kotlin.String, kotlin.Boolean>? declared in <root>.foo' type=kotlin.Function1<kotlin.String, kotlin.Boolean>? origin=null
+      RETURN type=kotlin.Nothing from='public final fun foo (filter: kotlin.Function1<kotlin.String, kotlin.Boolean>?): kotlin.String declared in <root>'
+        CONST String type=kotlin.String value="OK"
diff --git a/compiler/testData/codegen/box/sam/kt54600.ir.txt b/compiler/testData/codegen/box/sam/kt54600.ir.txt
new file mode 100644
index 00000000000..97f44ae2dda
--- /dev/null
+++ b/compiler/testData/codegen/box/sam/kt54600.ir.txt
@@ -0,0 +1,16 @@
+FILE fqName:<root> fileName:/box.kt
+  FUN name:box visibility:public modality:FINAL <> () returnType:kotlin.String
+    BLOCK_BODY
+      RETURN type=kotlin.Nothing from='public final fun box (): kotlin.String declared in <root>'
+        CALL 'public final fun foo (filter: kotlin.Function1<kotlin.String, kotlin.Boolean>?): kotlin.String declared in <root>' type=kotlin.String origin=null
+          filter: CONST Null type=kotlin.Nothing? value=null
+  FUN name:foo visibility:public modality:FINAL <> (filter:kotlin.Function1<kotlin.String, kotlin.Boolean>?) returnType:kotlin.String
+    VALUE_PARAMETER name:filter index:0 type:kotlin.Function1<kotlin.String, kotlin.Boolean>?
+    BLOCK_BODY
+      TYPE_OP type=kotlin.Unit origin=IMPLICIT_COERCION_TO_UNIT typeOperand=kotlin.Unit
+        CONSTRUCTOR_CALL 'public constructor <init> (filter: @[FlexibleNullability] <root>.Condition<in @[FlexibleNullability] kotlin.String?>?) declared in <root>.J' type=<root>.J origin=null
+          filter: TYPE_OP type=@[FlexibleNullability] <root>.Condition<kotlin.Any?>? origin=SAM_CONVERSION typeOperand=@[FlexibleNullability] <root>.Condition<kotlin.Any?>?
+            TYPE_OP type=@[FlexibleNullability] kotlin.Function1<@[ParameterName(name = 't')] kotlin.Any?, kotlin.Boolean>? origin=IMPLICIT_CAST typeOperand=@[FlexibleNullability] kotlin.Function1<@[ParameterName(name = 't')] kotlin.Any?, kotlin.Boolean>?
+              GET_VAR 'filter: kotlin.Function1<kotlin.String, kotlin.Boolean>? declared in <root>.foo' type=kotlin.Function1<kotlin.String, kotlin.Boolean>? origin=null
+      RETURN type=kotlin.Nothing from='public final fun foo (filter: kotlin.Function1<kotlin.String, kotlin.Boolean>?): kotlin.String declared in <root>'
+        CONST String type=kotlin.String value="OK"
diff --git a/compiler/testData/codegen/box/sam/kt54600.kt b/compiler/testData/codegen/box/sam/kt54600.kt
new file mode 100644
index 00000000000..7b96d0af73c
--- /dev/null
+++ b/compiler/testData/codegen/box/sam/kt54600.kt
@@ -0,0 +1,27 @@
+// TARGET_BACKEND: JVM
+// DUMP_IR
+// FILE: box.kt
+
+fun box(): String =
+    foo(null)
+
+fun foo(filter: ((String) -> Boolean)?): String {
+    J(filter)
+    return "OK"
+}
+
+// FILE: J.java
+
+public class J {
+    public J(Condition<? super String> filter) {
+        if (filter != null) {
+            filter.value("");
+        }
+    }
+}
+
+// FILE: Condition.java
+
+public interface Condition<T> {
+    boolean value(T t);
+}
diff --git a/compiler/testData/ir/irText/expressions/sam/samConversionsWithSmartCasts.ir.txt b/compiler/testData/ir/irText/expressions/sam/samConversionsWithSmartCasts.ir.txt
index 90f46390c80..21037d89b92 100644
--- a/compiler/testData/ir/irText/expressions/sam/samConversionsWithSmartCasts.ir.txt
+++ b/compiler/testData/ir/irText/expressions/sam/samConversionsWithSmartCasts.ir.txt
@@ -106,10 +106,9 @@ 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> () [primary] declared in <root>.J' type=<root>.J origin=null
         r: TYPE_OP type=@[FlexibleNullability] java.lang.Runnable? origin=SAM_CONVERSION typeOperand=@[FlexibleNullability] java.lang.Runnable?
-          TYPE_OP type=kotlin.Function0<kotlin.Unit> origin=IMPLICIT_NOTNULL typeOperand=kotlin.Function0<kotlin.Unit>
-            CALL 'public open fun id <T> (x: @[FlexibleNullability] T of <root>.J.id?): @[FlexibleNullability] T of <root>.J.id? declared in <root>.J' type=@[FlexibleNullability] kotlin.Function0<kotlin.Unit>? origin=null
-              <T>: @[FlexibleNullability] kotlin.Function0<kotlin.Unit>?
-              x: GET_VAR 'a: kotlin.Function0<kotlin.Unit> declared in <root>.test8' type=kotlin.Function0<kotlin.Unit> origin=null
+          CALL 'public open fun id <T> (x: @[FlexibleNullability] T of <root>.J.id?): @[FlexibleNullability] T of <root>.J.id? declared in <root>.J' type=@[FlexibleNullability] kotlin.Function0<kotlin.Unit>? origin=null
+            <T>: @[FlexibleNullability] kotlin.Function0<kotlin.Unit>?
+            x: GET_VAR 'a: kotlin.Function0<kotlin.Unit> declared in <root>.test8' type=kotlin.Function0<kotlin.Unit> origin=null
   FUN name:test9 visibility:public modality:FINAL <> () returnType:kotlin.Unit
     BLOCK_BODY
       CALL 'public open fun run1 (r: @[FlexibleNullability] java.lang.Runnable?): kotlin.Unit declared in <root>.J' type=kotlin.Unit origin=null
diff --git a/compiler/testData/ir/irText/expressions/sam/samConversionsWithSmartCasts.kt.txt b/compiler/testData/ir/irText/expressions/sam/samConversionsWithSmartCasts.kt.txt
index c0b64824632..a2b263c7356 100644
--- a/compiler/testData/ir/irText/expressions/sam/samConversionsWithSmartCasts.kt.txt
+++ b/compiler/testData/ir/irText/expressions/sam/samConversionsWithSmartCasts.kt.txt
@@ -58,9 +58,10 @@ fun test7(a: Function1<Int, Int>) {
 }
 
 fun test8(a: Function0<Unit>) {
-  J().run1(r = id<@FlexibleNullability Function0<Unit>?>(x = a) /*!! Function0<Unit> */ /*-> @FlexibleNullability Runnable? */)
+  J().run1(r = id<@FlexibleNullability Function0<Unit>?>(x = a) /*-> @FlexibleNullability Runnable? */)
 }
 
 fun test9() {
   J().run1(r = ::test9 /*-> @FlexibleNullability Runnable? */)
 }
+
diff --git a/compiler/tests-common-new/tests-gen/org/jetbrains/kotlin/test/runners/codegen/BlackBoxCodegenTestGenerated.java b/compiler/tests-common-new/tests-gen/org/jetbrains/kotlin/test/runners/codegen/BlackBoxCodegenTestGenerated.java
index bce4fc07ca5..31ba58d46c8 100644
--- a/compiler/tests-common-new/tests-gen/org/jetbrains/kotlin/test/runners/codegen/BlackBoxCodegenTestGenerated.java
+++ b/compiler/tests-common-new/tests-gen/org/jetbrains/kotlin/test/runners/codegen/BlackBoxCodegenTestGenerated.java
@@ -44909,6 +44909,12 @@ public class BlackBoxCodegenTestGenerated extends AbstractBlackBoxCodegenTest {
             runTest("compiler/testData/codegen/box/sam/kt52417.kt");
         }
 
+        @Test
+        @TestMetadata("kt54600.kt")
+        public void testKt54600() throws Exception {
+            runTest("compiler/testData/codegen/box/sam/kt54600.kt");
+        }
+
         @Test
         @TestMetadata("nonInlinedSamWrapper.kt")
         public void testNonInlinedSamWrapper() throws Exception {
diff --git a/compiler/tests-common-new/tests-gen/org/jetbrains/kotlin/test/runners/codegen/IrBlackBoxCodegenTestGenerated.java b/compiler/tests-common-new/tests-gen/org/jetbrains/kotlin/test/runners/codegen/IrBlackBoxCodegenTestGenerated.java
index 68a1a321b78..caf46188682 100644
--- a/compiler/tests-common-new/tests-gen/org/jetbrains/kotlin/test/runners/codegen/IrBlackBoxCodegenTestGenerated.java
+++ b/compiler/tests-common-new/tests-gen/org/jetbrains/kotlin/test/runners/codegen/IrBlackBoxCodegenTestGenerated.java
@@ -46523,6 +46523,12 @@ public class IrBlackBoxCodegenTestGenerated extends AbstractIrBlackBoxCodegenTes
             runTest("compiler/testData/codegen/box/sam/kt52417.kt");
         }
 
+        @Test
+        @TestMetadata("kt54600.kt")
+        public void testKt54600() throws Exception {
+            runTest("compiler/testData/codegen/box/sam/kt54600.kt");
+        }
+
         @Test
         @TestMetadata("nonInlinedSamWrapper.kt")
         public void testNonInlinedSamWrapper() throws Exception {
diff --git a/compiler/tests-gen/org/jetbrains/kotlin/codegen/LightAnalysisModeTestGenerated.java b/compiler/tests-gen/org/jetbrains/kotlin/codegen/LightAnalysisModeTestGenerated.java
index 78fd52cc640..a109d77bcc2 100644
--- a/compiler/tests-gen/org/jetbrains/kotlin/codegen/LightAnalysisModeTestGenerated.java
+++ b/compiler/tests-gen/org/jetbrains/kotlin/codegen/LightAnalysisModeTestGenerated.java
@@ -36225,6 +36225,11 @@ public class LightAnalysisModeTestGenerated extends AbstractLightAnalysisModeTes
             runTest("compiler/testData/codegen/box/sam/kt52417.kt");
         }
 
+        @TestMetadata("kt54600.kt")
+        public void testKt54600() throws Exception {
+            runTest("compiler/testData/codegen/box/sam/kt54600.kt");
+        }
+
         @TestMetadata("nonInlinedSamWrapper.kt")
         public void testNonInlinedSamWrapper() throws Exception {
             runTest("compiler/testData/codegen/box/sam/nonInlinedSamWrapper.kt");