diff --git a/src/vm/stack.cc b/src/vm/stack.cc
index eee209a..1a298f0 100644
--- a/src/vm/stack.cc
+++ b/src/vm/stack.cc
@@ -51,7 +51,11 @@ void Stack::push_fp()
 
 void Stack::pop_fp()
 {
+    if (fps_.size() == 1)
+        throw VMStackUnderflow();
 
+    stack_.resize(fps_.top());
+    fps_.pop();
 }
 
 } // tyche
diff --git a/src/vm/value.hh b/src/vm/value.hh
index 9009c4d..8039233 100644
--- a/src/vm/value.hh
+++ b/src/vm/value.hh
@@ -13,6 +13,8 @@ enum class Type : uint8_t
 
 class Value {
 public:
+    Value() : value_(std::monostate()) {}
+
     static Value CreateNil() { return Value(std::monostate()); }
     static Value CreateInteger(int32_t v) { return Value(v); }
     static Value CreateFloat(float f) { return Value(f); }