diff --git a/compiler/fir/cones/src/org/jetbrains/kotlin/fir/types/ConeTypeUtils.kt b/compiler/fir/cones/src/org/jetbrains/kotlin/fir/types/ConeTypeUtils.kt
index 1c211b3caac..250941f8890 100644
--- a/compiler/fir/cones/src/org/jetbrains/kotlin/fir/types/ConeTypeUtils.kt
+++ b/compiler/fir/cones/src/org/jetbrains/kotlin/fir/types/ConeTypeUtils.kt
@@ -65,6 +65,13 @@ fun ConeKotlinType.lowerBoundIfFlexible(): ConeSimpleKotlinType {
     }
 }
 
+fun ConeKotlinType.originalIfDefinitelyNotNullable(): ConeKotlinType {
+    return when (this) {
+        is ConeDefinitelyNotNullType -> original
+        else -> this
+    }
+}
+
 fun ConeIntersectionType.withAlternative(alternativeType: ConeKotlinType): ConeIntersectionType {
     return ConeIntersectionType(intersectedTypes, alternativeType)
 }
diff --git a/compiler/fir/resolve/src/org/jetbrains/kotlin/fir/resolve/calls/Arguments.kt b/compiler/fir/resolve/src/org/jetbrains/kotlin/fir/resolve/calls/Arguments.kt
index 0b47d97e587..1d61383cb85 100644
--- a/compiler/fir/resolve/src/org/jetbrains/kotlin/fir/resolve/calls/Arguments.kt
+++ b/compiler/fir/resolve/src/org/jetbrains/kotlin/fir/resolve/calls/Arguments.kt
@@ -6,8 +6,8 @@
 package org.jetbrains.kotlin.fir.resolve.calls
 
 import org.jetbrains.kotlin.fir.FirSession
-import org.jetbrains.kotlin.fir.declarations.FirFunction
 import org.jetbrains.kotlin.fir.declarations.FirCallableDeclaration
+import org.jetbrains.kotlin.fir.declarations.FirFunction
 import org.jetbrains.kotlin.fir.declarations.FirValueParameter
 import org.jetbrains.kotlin.fir.expressions.*
 import org.jetbrains.kotlin.fir.lookupTracker
@@ -540,7 +540,7 @@ fun FirExpression.isFunctional(
             // Make sure the contributed `invoke` is indeed a wanted functional type by checking if types are compatible.
             val expectedReturnType = classLikeExpectedFunctionType.returnType(session).lowerBoundIfFlexible()
             val returnTypeCompatible =
-                expectedReturnType is ConeTypeParameterType ||
+                expectedReturnType.originalIfDefinitelyNotNullable() is ConeTypeParameterType ||
                         AbstractTypeChecker.isSubtypeOf(
                             session.typeContext.newTypeCheckerState(
                                 errorTypesEqualToAnything = false,
@@ -560,7 +560,7 @@ fun FirExpression.isFunctional(
                 invokeSymbol.fir.valueParameters.zip(classLikeExpectedFunctionType.valueParameterTypesIncludingReceiver(session))
             return parameterPairs.all { (invokeParameter, expectedParameter) ->
                 val expectedParameterType = expectedParameter.lowerBoundIfFlexible()
-                expectedParameterType is ConeTypeParameterType ||
+                expectedParameterType.originalIfDefinitelyNotNullable() is ConeTypeParameterType ||
                         AbstractTypeChecker.isSubtypeOf(
                             session.typeContext.newTypeCheckerState(
                                 errorTypesEqualToAnything = false,