diff --git a/compiler/fir/resolve/src/org/jetbrains/kotlin/fir/resolve/inference/ConstraintSystemCompleter.kt b/compiler/fir/resolve/src/org/jetbrains/kotlin/fir/resolve/inference/ConstraintSystemCompleter.kt
index e316cf9f3ff..2750288b867 100644
--- a/compiler/fir/resolve/src/org/jetbrains/kotlin/fir/resolve/inference/ConstraintSystemCompleter.kt
+++ b/compiler/fir/resolve/src/org/jetbrains/kotlin/fir/resolve/inference/ConstraintSystemCompleter.kt
@@ -188,14 +188,15 @@ class ConstraintSystemCompleter(components: BodyResolveComponents, private val c
 
         // We assume useBuilderInferenceWithoutAnnotation = true for FIR
 
+        val builder = getBuilder()
         for (argument in lambdaArguments) {
             val notFixedInputTypeVariables = argument.inputTypes
-                .map { it.extractTypeVariables() }.flatten().filter { it !in fixedTypeVariables }
+                .flatMap { it.extractTypeVariables() }.filter { it !in fixedTypeVariables }
 
             if (notFixedInputTypeVariables.isEmpty()) continue
 
             for (variable in notFixedInputTypeVariables) {
-                getBuilder().markPostponedVariable(notFixedTypeVariables.getValue(variable).typeVariable)
+                builder.markPostponedVariable(notFixedTypeVariables.getValue(variable).typeVariable)
             }
 
             analyze(argument)
diff --git a/compiler/resolution/src/org/jetbrains/kotlin/resolve/calls/inference/components/KotlinConstraintSystemCompleter.kt b/compiler/resolution/src/org/jetbrains/kotlin/resolve/calls/inference/components/KotlinConstraintSystemCompleter.kt
index ae0ad199d4c..408a44778ab 100644
--- a/compiler/resolution/src/org/jetbrains/kotlin/resolve/calls/inference/components/KotlinConstraintSystemCompleter.kt
+++ b/compiler/resolution/src/org/jetbrains/kotlin/resolve/calls/inference/components/KotlinConstraintSystemCompleter.kt
@@ -216,17 +216,18 @@ class KotlinConstraintSystemCompleter(
         val useBuilderInferenceWithoutAnnotation =
             languageVersionSettings.supportsFeature(LanguageFeature.UseBuilderInferenceWithoutAnnotation)
 
+        val builder = getBuilder()
         for (argument in lambdaArguments) {
             if (!argument.atom.hasBuilderInferenceAnnotation && !useBuilderInferenceWithoutAnnotation)
                 continue
 
             val notFixedInputTypeVariables = argument.inputTypes
-                .map { it.extractTypeVariables() }.flatten().filter { it !in fixedTypeVariables }
+                .flatMap { it.extractTypeVariables() }.filter { it !in fixedTypeVariables }
 
             if (notFixedInputTypeVariables.isEmpty()) continue
 
             for (variable in notFixedInputTypeVariables) {
-                getBuilder().markPostponedVariable(notFixedTypeVariables.getValue(variable).typeVariable)
+                builder.markPostponedVariable(notFixedTypeVariables.getValue(variable).typeVariable)
             }
 
             analyze(argument)