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 bc88167f326..b3ca25031a4 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
@@ -44,6 +44,7 @@ import org.jetbrains.kotlin.ir.types.impl.IrSimpleTypeImpl
 import org.jetbrains.kotlin.ir.types.impl.makeTypeProjection
 import org.jetbrains.kotlin.ir.util.*
 import org.jetbrains.kotlin.name.Name
+import org.jetbrains.kotlin.psi2ir.generators.implicitCastTo
 import org.jetbrains.kotlin.types.AbstractTypeChecker
 import org.jetbrains.kotlin.types.Variance
 import org.jetbrains.kotlin.types.model.TypeVariance
@@ -443,7 +444,25 @@ internal class AdapterGenerator(
         val samType = samFirType.toIrType(ConversionTypeContext.DEFAULT)
         // Make sure the converted IrType owner indeed has a single abstract method, since FunctionReferenceLowering relies on it.
         if (!samType.isSamType) return this
-        return IrTypeOperatorCallImpl(this.startOffset, this.endOffset, samType, IrTypeOperator.SAM_CONVERSION, samType, this)
+        return IrTypeOperatorCallImpl(
+            this.startOffset, this.endOffset, samType, IrTypeOperator.SAM_CONVERSION, samType,
+            castArgumentToFunctionalInterfaceForSamType(this, argument.typeRef.coneType, samFirType)
+        )
+    }
+
+    // See org.jetbrains.kotlin.psi2ir.generators.ArgumentsGenerationUtilsKt.castArgumentToFunctionalInterfaceForSamType (K1 counterpart)
+    private fun castArgumentToFunctionalInterfaceForSamType(
+        argument: IrExpression,
+        argumentConeType: ConeKotlinType,
+        samType: ConeKotlinType
+    ): IrExpression {
+        val coneKotlinFunctionType = getFunctionTypeForPossibleSamType(samType) ?: 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()
+        return argument.implicitCastTo(irFunctionType)
     }
 
     // This function is mostly a mirror of org.jetbrains.kotlin.backend.common.SamTypeApproximator.removeExternalProjections
diff --git a/compiler/testData/ir/irText/expressions/chainedFunSuspendConversionForSimpleExpression.fir.ir.txt b/compiler/testData/ir/irText/expressions/chainedFunSuspendConversionForSimpleExpression.fir.ir.txt
index da398e97deb..6772ebf733e 100644
--- a/compiler/testData/ir/irText/expressions/chainedFunSuspendConversionForSimpleExpression.fir.ir.txt
+++ b/compiler/testData/ir/irText/expressions/chainedFunSuspendConversionForSimpleExpression.fir.ir.txt
@@ -32,33 +32,36 @@ FILE fqName:<root> fileName:/chainedFunSuspendConversionForSimpleExpression.kt
     BLOCK_BODY
       CALL 'public final fun foo (s: <root>.SuspendRunnable): kotlin.Unit declared in <root>' type=kotlin.Unit origin=null
         s: TYPE_OP type=<root>.SuspendRunnable origin=SAM_CONVERSION typeOperand=<root>.SuspendRunnable
-          BLOCK type=kotlin.coroutines.SuspendFunction0<kotlin.Unit> origin=SUSPEND_CONVERSION
-            FUN ADAPTER_FOR_SUSPEND_CONVERSION name:suspendConversion visibility:local modality:FINAL <> ($receiver:kotlin.Function0<kotlin.Unit>) returnType:kotlin.Unit [suspend]
-              $receiver: VALUE_PARAMETER ADAPTER_PARAMETER_FOR_SUSPEND_CONVERSION name:callee type:kotlin.Function0<kotlin.Unit>
-              BLOCK_BODY
-                CALL 'public abstract fun invoke (): R of kotlin.Function0 [operator] declared in kotlin.Function0' type=kotlin.Unit origin=null
-                  $this: GET_VAR 'callee: kotlin.Function0<kotlin.Unit> declared in <root>.test.suspendConversion' type=kotlin.Function0<kotlin.Unit> origin=null
-            FUNCTION_REFERENCE 'local final fun suspendConversion (): kotlin.Unit [suspend] declared in <root>.test' type=kotlin.coroutines.SuspendFunction0<kotlin.Unit> origin=SUSPEND_CONVERSION reflectionTarget=null
-              $receiver: GET_VAR 'f: kotlin.Function0<kotlin.Unit> declared in <root>.test' type=kotlin.Function0<kotlin.Unit> origin=null
+          TYPE_OP type=kotlin.coroutines.SuspendFunction0<kotlin.Unit> origin=IMPLICIT_CAST typeOperand=kotlin.coroutines.SuspendFunction0<kotlin.Unit>
+            BLOCK type=kotlin.coroutines.SuspendFunction0<kotlin.Unit> origin=SUSPEND_CONVERSION
+              FUN ADAPTER_FOR_SUSPEND_CONVERSION name:suspendConversion visibility:local modality:FINAL <> ($receiver:kotlin.Function0<kotlin.Unit>) returnType:kotlin.Unit [suspend]
+                $receiver: VALUE_PARAMETER ADAPTER_PARAMETER_FOR_SUSPEND_CONVERSION name:callee type:kotlin.Function0<kotlin.Unit>
+                BLOCK_BODY
+                  CALL 'public abstract fun invoke (): R of kotlin.Function0 [operator] declared in kotlin.Function0' type=kotlin.Unit origin=null
+                    $this: GET_VAR 'callee: kotlin.Function0<kotlin.Unit> declared in <root>.test.suspendConversion' type=kotlin.Function0<kotlin.Unit> origin=null
+              FUNCTION_REFERENCE 'local final fun suspendConversion (): kotlin.Unit [suspend] declared in <root>.test' type=kotlin.coroutines.SuspendFunction0<kotlin.Unit> origin=SUSPEND_CONVERSION reflectionTarget=null
+                $receiver: GET_VAR 'f: kotlin.Function0<kotlin.Unit> declared in <root>.test' type=kotlin.Function0<kotlin.Unit> origin=null
       CALL 'public final fun foo (s: <root>.SuspendRunnable): kotlin.Unit declared in <root>' type=kotlin.Unit origin=null
         s: TYPE_OP type=<root>.SuspendRunnable origin=SAM_CONVERSION typeOperand=<root>.SuspendRunnable
-          BLOCK type=kotlin.coroutines.SuspendFunction0<kotlin.Unit> origin=SUSPEND_CONVERSION
-            FUN ADAPTER_FOR_SUSPEND_CONVERSION name:suspendConversion visibility:local modality:FINAL <> ($receiver:kotlin.Function0<kotlin.Unit>) returnType:kotlin.Unit [suspend]
-              $receiver: VALUE_PARAMETER ADAPTER_PARAMETER_FOR_SUSPEND_CONVERSION name:callee type:kotlin.Function0<kotlin.Unit>
-              BLOCK_BODY
-                CALL 'public abstract fun invoke (): R of kotlin.Function0 [operator] declared in kotlin.Function0' type=kotlin.Unit origin=null
-                  $this: GET_VAR 'callee: kotlin.Function0<kotlin.Unit> declared in <root>.test.suspendConversion' type=kotlin.Function0<kotlin.Unit> origin=null
-            FUNCTION_REFERENCE 'local final fun suspendConversion (): kotlin.Unit [suspend] declared in <root>.test' type=kotlin.coroutines.SuspendFunction0<kotlin.Unit> origin=SUSPEND_CONVERSION reflectionTarget=null
-              $receiver: CALL 'public final fun bar (): kotlin.Function0<kotlin.Unit> declared in <root>' type=kotlin.Function0<kotlin.Unit> origin=null
+          TYPE_OP type=kotlin.coroutines.SuspendFunction0<kotlin.Unit> origin=IMPLICIT_CAST typeOperand=kotlin.coroutines.SuspendFunction0<kotlin.Unit>
+            BLOCK type=kotlin.coroutines.SuspendFunction0<kotlin.Unit> origin=SUSPEND_CONVERSION
+              FUN ADAPTER_FOR_SUSPEND_CONVERSION name:suspendConversion visibility:local modality:FINAL <> ($receiver:kotlin.Function0<kotlin.Unit>) returnType:kotlin.Unit [suspend]
+                $receiver: VALUE_PARAMETER ADAPTER_PARAMETER_FOR_SUSPEND_CONVERSION name:callee type:kotlin.Function0<kotlin.Unit>
+                BLOCK_BODY
+                  CALL 'public abstract fun invoke (): R of kotlin.Function0 [operator] declared in kotlin.Function0' type=kotlin.Unit origin=null
+                    $this: GET_VAR 'callee: kotlin.Function0<kotlin.Unit> declared in <root>.test.suspendConversion' type=kotlin.Function0<kotlin.Unit> origin=null
+              FUNCTION_REFERENCE 'local final fun suspendConversion (): kotlin.Unit [suspend] declared in <root>.test' type=kotlin.coroutines.SuspendFunction0<kotlin.Unit> origin=SUSPEND_CONVERSION reflectionTarget=null
+                $receiver: CALL 'public final fun bar (): kotlin.Function0<kotlin.Unit> declared in <root>' type=kotlin.Function0<kotlin.Unit> origin=null
       VAR name:t type:kotlin.Function0<kotlin.Unit> [var]
         GET_VAR 'f: kotlin.Function0<kotlin.Unit> declared in <root>.test' type=kotlin.Function0<kotlin.Unit> origin=null
       CALL 'public final fun foo (s: <root>.SuspendRunnable): kotlin.Unit declared in <root>' type=kotlin.Unit origin=null
         s: TYPE_OP type=<root>.SuspendRunnable origin=SAM_CONVERSION typeOperand=<root>.SuspendRunnable
-          BLOCK type=kotlin.coroutines.SuspendFunction0<kotlin.Unit> origin=SUSPEND_CONVERSION
-            FUN ADAPTER_FOR_SUSPEND_CONVERSION name:suspendConversion visibility:local modality:FINAL <> ($receiver:kotlin.Function0<kotlin.Unit>) returnType:kotlin.Unit [suspend]
-              $receiver: VALUE_PARAMETER ADAPTER_PARAMETER_FOR_SUSPEND_CONVERSION name:callee type:kotlin.Function0<kotlin.Unit>
-              BLOCK_BODY
-                CALL 'public abstract fun invoke (): R of kotlin.Function0 [operator] declared in kotlin.Function0' type=kotlin.Unit origin=null
-                  $this: GET_VAR 'callee: kotlin.Function0<kotlin.Unit> declared in <root>.test.suspendConversion' type=kotlin.Function0<kotlin.Unit> origin=null
-            FUNCTION_REFERENCE 'local final fun suspendConversion (): kotlin.Unit [suspend] declared in <root>.test' type=kotlin.coroutines.SuspendFunction0<kotlin.Unit> origin=SUSPEND_CONVERSION reflectionTarget=null
-              $receiver: GET_VAR 'var t: kotlin.Function0<kotlin.Unit> [var] declared in <root>.test' type=kotlin.Function0<kotlin.Unit> origin=null
+          TYPE_OP type=kotlin.coroutines.SuspendFunction0<kotlin.Unit> origin=IMPLICIT_CAST typeOperand=kotlin.coroutines.SuspendFunction0<kotlin.Unit>
+            BLOCK type=kotlin.coroutines.SuspendFunction0<kotlin.Unit> origin=SUSPEND_CONVERSION
+              FUN ADAPTER_FOR_SUSPEND_CONVERSION name:suspendConversion visibility:local modality:FINAL <> ($receiver:kotlin.Function0<kotlin.Unit>) returnType:kotlin.Unit [suspend]
+                $receiver: VALUE_PARAMETER ADAPTER_PARAMETER_FOR_SUSPEND_CONVERSION name:callee type:kotlin.Function0<kotlin.Unit>
+                BLOCK_BODY
+                  CALL 'public abstract fun invoke (): R of kotlin.Function0 [operator] declared in kotlin.Function0' type=kotlin.Unit origin=null
+                    $this: GET_VAR 'callee: kotlin.Function0<kotlin.Unit> declared in <root>.test.suspendConversion' type=kotlin.Function0<kotlin.Unit> origin=null
+              FUNCTION_REFERENCE 'local final fun suspendConversion (): kotlin.Unit [suspend] declared in <root>.test' type=kotlin.coroutines.SuspendFunction0<kotlin.Unit> origin=SUSPEND_CONVERSION reflectionTarget=null
+                $receiver: GET_VAR 'var t: kotlin.Function0<kotlin.Unit> [var] declared in <root>.test' type=kotlin.Function0<kotlin.Unit> origin=null
diff --git a/compiler/testData/ir/irText/firProblems/kt19251.fir.ir.txt b/compiler/testData/ir/irText/firProblems/kt19251.fir.ir.txt
index 707632c37af..952033b40fd 100644
--- a/compiler/testData/ir/irText/firProblems/kt19251.fir.ir.txt
+++ b/compiler/testData/ir/irText/firProblems/kt19251.fir.ir.txt
@@ -18,9 +18,10 @@ FILE fqName:<root> fileName:/test.kt
             $this: GET_VAR 'val map: kotlin.collections.MutableMap<<root>.Fun, kotlin.String> [val] declared in <root>.box' type=kotlin.collections.MutableMap<<root>.Fun, kotlin.String> origin=null
             p0: GET_VAR 'val fn: <root>.Fun [val] declared in <root>.box' type=<root>.Fun origin=null
             p1: TYPE_OP type=@[EnhancedNullability] java.util.function.Function<kotlin.Any?, @[EnhancedNullability] kotlin.String> origin=SAM_CONVERSION typeOperand=@[EnhancedNullability] java.util.function.Function<kotlin.Any?, @[EnhancedNullability] kotlin.String>
-              FUN_EXPR type=kotlin.Function1<@[EnhancedNullability] <root>.Fun, @[EnhancedNullability] kotlin.String> origin=LAMBDA
-                FUN LOCAL_FUNCTION_FOR_LAMBDA name:<anonymous> visibility:local modality:FINAL <> (it:@[EnhancedNullability] <root>.Fun) returnType:@[EnhancedNullability] kotlin.String
-                  VALUE_PARAMETER name:it index:0 type:@[EnhancedNullability] <root>.Fun
-                  BLOCK_BODY
-                    RETURN type=kotlin.Nothing from='local final fun <anonymous> (it: @[EnhancedNullability] <root>.Fun): @[EnhancedNullability] kotlin.String declared in <root>.box'
-                      CONST String type=kotlin.String value="OK"
+              TYPE_OP type=kotlin.Function1<@[EnhancedNullability] kotlin.Any?, @[EnhancedNullability] kotlin.String> origin=IMPLICIT_CAST typeOperand=kotlin.Function1<@[EnhancedNullability] kotlin.Any?, @[EnhancedNullability] kotlin.String>
+                FUN_EXPR type=kotlin.Function1<@[EnhancedNullability] <root>.Fun, @[EnhancedNullability] kotlin.String> origin=LAMBDA
+                  FUN LOCAL_FUNCTION_FOR_LAMBDA name:<anonymous> visibility:local modality:FINAL <> (it:@[EnhancedNullability] <root>.Fun) returnType:@[EnhancedNullability] kotlin.String
+                    VALUE_PARAMETER name:it index:0 type:@[EnhancedNullability] <root>.Fun
+                    BLOCK_BODY
+                      RETURN type=kotlin.Nothing from='local final fun <anonymous> (it: @[EnhancedNullability] <root>.Fun): @[EnhancedNullability] kotlin.String declared in <root>.box'
+                        CONST String type=kotlin.String value="OK"
diff --git a/compiler/testData/ir/irText/firProblems/kt19251.fir.kt.txt b/compiler/testData/ir/irText/firProblems/kt19251.fir.kt.txt
index 5425b0b218b..cf710bd0530 100644
--- a/compiler/testData/ir/irText/firProblems/kt19251.fir.kt.txt
+++ b/compiler/testData/ir/irText/firProblems/kt19251.fir.kt.txt
@@ -7,5 +7,5 @@ fun box(): String {
   return map.computeIfAbsent(p0 = fn, p1 = local fun <anonymous>(it: @EnhancedNullability Fun): @EnhancedNullability String {
     return "OK"
   }
- /*-> @EnhancedNullability Function<Any?, @EnhancedNullability String> */) /*!! String */
+ /*as Function1<@EnhancedNullability Any?, @EnhancedNullability String> */ /*-> @EnhancedNullability Function<Any?, @EnhancedNullability String> */) /*!! String */
 }