diff --git a/compiler/fir/resolve/src/org/jetbrains/kotlin/fir/resolve/SamResolution.kt b/compiler/fir/resolve/src/org/jetbrains/kotlin/fir/resolve/SamResolution.kt
index fb8f6ef3bc1..c0a1020eb43 100644
--- a/compiler/fir/resolve/src/org/jetbrains/kotlin/fir/resolve/SamResolution.kt
+++ b/compiler/fir/resolve/src/org/jetbrains/kotlin/fir/resolve/SamResolution.kt
@@ -41,6 +41,8 @@ import org.jetbrains.kotlin.name.CallableId
 import org.jetbrains.kotlin.name.Name
 import org.jetbrains.kotlin.name.StandardClassIds
 import org.jetbrains.kotlin.types.Variance
+import org.jetbrains.kotlin.utils.addToStdlib.runIf
+import org.jetbrains.kotlin.utils.addToStdlib.unreachableBranch
 
 private val SAM_PARAMETER_NAME = Name.identifier("function")
 
@@ -73,14 +75,13 @@ class FirSamResolver(
                 val upperType = getFunctionTypeForPossibleSamType(type.upperBound) ?: return null
                 ConeFlexibleType(lowerType.lowerBoundIfFlexible(), upperType.upperBoundIfFlexible())
             }
-            is ConeStubType -> null
-            // TODO: support those types as well
-            is ConeTypeParameterType, is ConeTypeVariableType,
+
+            is ConeStubType, is ConeTypeParameterType, is ConeTypeVariableType,
             is ConeCapturedType, is ConeDefinitelyNotNullType, is ConeIntersectionType,
             is ConeIntegerLiteralType,
             -> null
-            // TODO: Thing of getting rid of this branch since ConeLookupTagBasedType should be a sealed class
-            is ConeLookupTagBasedType -> null
+
+            is ConeLookupTagBasedType -> unreachableBranch(type)
         }
     }
 
@@ -282,7 +283,6 @@ private fun FirRegularClass.getSingleAbstractMethodOrNull(
     session: FirSession,
     scopeSession: ScopeSession,
 ): FirSimpleFunction? {
-    // TODO: restrict to Java interfaces
     if (classKind != ClassKind.INTERFACE || hasMoreThenOneAbstractFunctionOrHasAbstractProperty()) return null
 
     val samCandidateNames = computeSamCandidateNames(session)
diff --git a/core/util.runtime/src/org/jetbrains/kotlin/utils/addToStdlib.kt b/core/util.runtime/src/org/jetbrains/kotlin/utils/addToStdlib.kt
index ef56069fdaa..a5de062f2cd 100644
--- a/core/util.runtime/src/org/jetbrains/kotlin/utils/addToStdlib.kt
+++ b/core/util.runtime/src/org/jetbrains/kotlin/utils/addToStdlib.kt
@@ -334,3 +334,10 @@ private inline fun <T, R> Iterable<T>.zipWithDefault(other: Iterable<R>, leftDef
 fun <T, R> Iterable<T>.zipWithNulls(other: Iterable<R>): List<Pair<T?, R?>> {
     return zipWithDefault(other, { null }, { null })
 }
+
+/**
+ * Use this function to indicate that some when branch is semantically unreachable
+ */
+fun unreachableBranch(argument: Any?): Nothing {
+    error("This argument should've been processed by previous when branches but it wasn't: $argument")
+}