diff --git a/usvm-core/src/main/kotlin/org/usvm/CallStack.kt b/usvm-core/src/main/kotlin/org/usvm/CallStack.kt
index e72b0eb27..ca615309c 100644
--- a/usvm-core/src/main/kotlin/org/usvm/CallStack.kt
+++ b/usvm-core/src/main/kotlin/org/usvm/CallStack.kt
@@ -41,7 +41,9 @@ class UCallStack<Method, Statement> private constructor(
             .zipWithNext { first, second -> UStackTraceFrame<Method, Statement>(first.method, second.returnSite!!) }
             .toMutableList()
 
-        return stacktrace + UStackTraceFrame(stack.last().method, currentInstruction)
+        stacktrace += UStackTraceFrame(stack.last().method, currentInstruction)
+
+        return stacktrace
     }
 
     override fun toString(): String {
diff --git a/usvm-core/src/main/kotlin/org/usvm/ps/ExceptionPropagationPathSelector.kt b/usvm-core/src/main/kotlin/org/usvm/ps/ExceptionPropagationPathSelector.kt
index 305d90961..f29107b14 100644
--- a/usvm-core/src/main/kotlin/org/usvm/ps/ExceptionPropagationPathSelector.kt
+++ b/usvm-core/src/main/kotlin/org/usvm/ps/ExceptionPropagationPathSelector.kt
@@ -15,13 +15,13 @@ class ExceptionPropagationPathSelector<State : UState<*, *, *, *>>(
     // to determine whether some state is already in the queue or not
     // without extra time consumption.
     // We use only keys from this map.
-    private val exceptionalStates = IdentityHashMap<State, Any?>()
+    private val exceptionalStates = IdentityHashMap<State, Nothing>()
 
     // An identity map of the states that were added in the internal selector.
     // That means that these states present not only in the internal queue, but in
     // the queue of the selector, and we have to process them as well.
     // We use only keys from this map.
-    private val statesInSelector = IdentityHashMap<State, Any?>()
+    private val statesInSelector = IdentityHashMap<State, Nothing>()
 
     override fun isEmpty(): Boolean = exceptionalStates.isEmpty() && selector.isEmpty()