diff --git a/compiler/fir/resolve/src/org/jetbrains/kotlin/fir/resolve/transformers/FirCallCompletionResultsWriterTransformer.kt b/compiler/fir/resolve/src/org/jetbrains/kotlin/fir/resolve/transformers/FirCallCompletionResultsWriterTransformer.kt
index 0c9b5c8..f95e717 100644
--- a/compiler/fir/resolve/src/org/jetbrains/kotlin/fir/resolve/transformers/FirCallCompletionResultsWriterTransformer.kt
+++ b/compiler/fir/resolve/src/org/jetbrains/kotlin/fir/resolve/transformers/FirCallCompletionResultsWriterTransformer.kt
@@ -812,8 +812,9 @@
         candidate: Candidate,
     ): List<FirTypeProjection> {
         val typeArguments = computeTypeArgumentTypes(candidate)
-            .mapIndexed { index, type ->
+            .mapIndexed { index, typeFromFinalSubstitutor ->
                 val argument = access.typeArguments.getOrNull(index)
+                val type = typeFromFinalSubstitutor.chooseActualExplicitArgumentIfResultWasMadeFlexibleSynthetically(argument)
                 val sourceForTypeArgument = argument?.source
                     ?: access.calleeReference.source?.fakeElement(KtFakeSourceElementKind.ImplicitTypeArgument)
                 when (argument) {
@@ -847,6 +848,19 @@
         } else typeArguments
     }
 
+    /**
+     * @see org.jetbrains.kotlin.fir.expressions.ExplicitTypeArgumentIfMadeFlexibleSyntheticallyTypeAttribute
+     * TODO: Get rid of this function once KT-59138 is fixed and the relevant feature for disabling it will be removed
+     */
+    private fun ConeKotlinType.chooseActualExplicitArgumentIfResultWasMadeFlexibleSynthetically(
+        argument: FirTypeProjection?,
+    ): ConeKotlinType {
+        if (this !is ConeFlexibleType) return this
+        if (argument !is FirTypeProjectionWithVariance) return this
+
+        return argument.typeRef.coneType
+    }
+
     private fun computeTypeArgumentTypes(
         candidate: Candidate,
     ): List<ConeKotlinType> {
diff --git a/compiler/testData/diagnostics/tests/samConversions/samConversionToGenericWrongNullability.fir.diag.txt b/compiler/testData/diagnostics/tests/samConversions/samConversionToGenericWrongNullability.fir.diag.txt
index 9cf721c..b26daae 100644
--- a/compiler/testData/diagnostics/tests/samConversions/samConversionToGenericWrongNullability.fir.diag.txt
+++ b/compiler/testData/diagnostics/tests/samConversions/samConversionToGenericWrongNullability.fir.diag.txt
@@ -1,5 +1,19 @@
+/test.kt:(194,216): warning: Argument type mismatch: actual type is 'kotlin.String?', but 'kotlin.String' was expected. This will become an error in a future release.
+
+/test.kt:(260,282): warning: Argument type mismatch: actual type is 'kotlin.String?', but 'kotlin.String' was expected. This will become an error in a future release.
+
+/test.kt:(321,358): warning: Argument type mismatch: actual type is 'kotlin.String?', but 'kotlin.String' was expected. This will become an error in a future release.
+
 /test.kt:(416,453): warning: Argument type mismatch: actual type is 'kotlin.String?', but 'kotlin.String' was expected. This will become an error in a future release.
 
+/test.kt:(510,592): warning: Argument type mismatch: actual type is 'kotlin.String?', but 'kotlin.String' was expected. This will become an error in a future release.
+
+/test.kt:(657,679): warning: Argument type mismatch: actual type is 'kotlin.String?', but 'kotlin.String' was expected. This will become an error in a future release.
+
+/test.kt:(710,732): warning: Argument type mismatch: actual type is 'kotlin.String?', but 'kotlin.String' was expected. This will become an error in a future release.
+
+/test.kt:(787,809): warning: Argument type mismatch: actual type is 'kotlin.String?', but 'kotlin.String' was expected. This will become an error in a future release.
+
 /test.kt:(1194,1216): warning: Argument type mismatch: actual type is 'kotlin.String?', but 'kotlin.String' was expected. This will become an error in a future release.
 
 /test.kt:(1299,1321): error: Return type mismatch: expected 'kotlin.String', actual 'kotlin.String?'.
@@ -12,10 +26,14 @@
 
 /test.kt:(1458,1480): error: Return type mismatch: expected 'kotlin.String', actual 'kotlin.String?'.
 
+/test.kt:(1596,1618): warning: Argument type mismatch: actual type is 'kotlin.String?', but 'kotlin.String' was expected. This will become an error in a future release.
+
 /test.kt:(1710,1810): error: Argument type mismatch: actual type is 'kotlin.String!', but 'kotlin.Function0<ERROR CLASS: Unknown return lambda parameter type>' was expected.
 
 /test.kt:(1710,1810): error: Argument type mismatch: actual type is 'kotlin.String!', but 'kotlin.Function0<kotlin.String?>' was expected.
 
+/test.kt:(1875,1897): warning: Argument type mismatch: actual type is 'kotlin.String?', but 'kotlin.String' was expected. This will become an error in a future release.
+
 /test.kt:(1976,1983): error: Return type of 'get' is not a subtype of the return type of the overridden member 'fun get(): String'.
 
 /test.kt:(2069,2072): error: Return type of 'get' is not a subtype of the return type of the overridden member 'fun get(): String'.
@@ -34,3 +52,9 @@
 /edge-cases.kt:(491,513): error: Argument type mismatch: actual type is 'kotlin.String?', but 'kotlin.Unit' was expected.
 
 /edge-cases.kt:(570,634): error: Argument type mismatch: actual type is 'kotlin.Unit', but 'kotlin.String!' was expected.
+
+/edge-cases.kt:(700,707): warning: Argument type mismatch: actual type is 'T?', but 'T' was expected. This will become an error in a future release.
+
+/edge-cases.kt:(797,804): warning: Argument type mismatch: actual type is 'T?', but 'T' was expected. This will become an error in a future release.
+
+/edge-cases.kt:(920,949): warning: Argument type mismatch: actual type is 'kotlin.String?', but 'kotlin.String' was expected. This will become an error in a future release.
diff --git a/compiler/testData/diagnostics/tests/samConversions/samConversionToGenericWrongNullability.fir.kt b/compiler/testData/diagnostics/tests/samConversions/samConversionToGenericWrongNullability.fir.kt
index bb3f54b..e949267 100644
--- a/compiler/testData/diagnostics/tests/samConversions/samConversionToGenericWrongNullability.fir.kt
+++ b/compiler/testData/diagnostics/tests/samConversions/samConversionToGenericWrongNullability.fir.kt
@@ -33,15 +33,15 @@
 
 fun main() {
     Supplier<String> {
-        returnNullableString()
+        <!TYPE_MISMATCH_WHEN_FLEXIBILITY_CHANGES!>returnNullableString()<!>
     }
 
     Supplier<StringAlias> {
-        returnNullableString()
+        <!TYPE_MISMATCH_WHEN_FLEXIBILITY_CHANGES!>returnNullableString()<!>
     }
 
     Supplier<String> {
-        TestValueProvider.getNullableString()
+        <!TYPE_MISMATCH_WHEN_FLEXIBILITY_CHANGES!>TestValueProvider.getNullableString()<!>
     }
 
     val sam: Supplier<String> = Supplier{
@@ -50,17 +50,17 @@
 
     Supplier<String> {
         val x = 1
-        when(x) {
+        <!TYPE_MISMATCH_WHEN_FLEXIBILITY_CHANGES!>when(x) {
             1 -> returnNullableString()
             else -> ""
-        }
+        }<!>
     }
 
     Supplier<String> {
-        if (true) return@Supplier returnNullableString()
-        run { return@Supplier returnNullableString() }
+        if (true) return@Supplier <!TYPE_MISMATCH_WHEN_FLEXIBILITY_CHANGES!>returnNullableString()<!>
+        run { return@Supplier <!TYPE_MISMATCH_WHEN_FLEXIBILITY_CHANGES!>returnNullableString()<!> }
         try {
-            if (true) return@Supplier returnNullableString()
+            if (true) return@Supplier <!TYPE_MISMATCH_WHEN_FLEXIBILITY_CHANGES!>returnNullableString()<!>
             2
         } finally {
             Unit
@@ -104,7 +104,7 @@
 
     Supplier<String>(
         fun(): String? {
-            if (true) return returnNullableString()
+            if (true) return <!TYPE_MISMATCH_WHEN_FLEXIBILITY_CHANGES!>returnNullableString()<!>
             return ""
         }
     )
@@ -117,7 +117,7 @@
     }
 
     Supplier<String> {
-        if (true) return@Supplier returnNullableString()
+        if (true) return@Supplier <!TYPE_MISMATCH_WHEN_FLEXIBILITY_CHANGES!>returnNullableString()<!>
         ""
     }
 
@@ -191,13 +191,13 @@
 
 fun <T: Number> test1(x: T) {
     Supplier<T> {
-        x.foo()
+        <!TYPE_MISMATCH_WHEN_FLEXIBILITY_CHANGES!>x.foo()<!>
     }
 }
 
 fun <T> test2(x: T) where T: Any?, T: Comparable<T> {
     Supplier<T> {
-        x.foo()
+        <!TYPE_MISMATCH_WHEN_FLEXIBILITY_CHANGES!>x.foo()<!>
     }
 }
 
@@ -207,6 +207,6 @@
 
 fun test()  {
     Supplier<String> {
-        returnNullableString().foo2()
+        <!TYPE_MISMATCH_WHEN_FLEXIBILITY_CHANGES!>returnNullableString().foo2()<!>
     }
 }
diff --git a/compiler/testData/diagnostics/tests/samConversions/samConversionWithJavaFlexibleType.fir.kt b/compiler/testData/diagnostics/tests/samConversions/samConversionWithJavaFlexibleType.fir.kt
index 1a2f537..45e7381 100644
--- a/compiler/testData/diagnostics/tests/samConversions/samConversionWithJavaFlexibleType.fir.kt
+++ b/compiler/testData/diagnostics/tests/samConversions/samConversionWithJavaFlexibleType.fir.kt
@@ -14,7 +14,7 @@
 
 fun test(){
     Supplier<String> {
-        JavaBox(null).a
+        <!TYPE_MISMATCH_WHEN_FLEXIBILITY_CHANGES!>JavaBox(null).a<!>
     }
 
     val sam : Supplier<String> = Supplier {