diff --git a/src/assembly_scanner.cpp b/src/assembly_scanner.cpp
index 073d489..750ff86 100644
--- a/src/assembly_scanner.cpp
+++ b/src/assembly_scanner.cpp
@@ -18,13 +18,11 @@ using std::string_view_literals::operator""sv;
     exit(EXIT_FAILURE);
 }
 
-const std::vector<instruction>& assembly_scanner::get_fragments() {
-    if (m_fragments.has_value()) {
-        return *m_fragments;
+const std::vector<instruction>& assembly_scanner::get_instructions() {
+    if (!m_instructions.empty()) {
+        return m_instructions;
     }
 
-    m_fragments.emplace(std::vector<instruction>());
-
     // We need to do two passes: one to resolve labels, and one to assign targets to jumps. During the first pass, the
     // fragments are actually constructed. However, jumps may not have valid targets yet, so we need some way to store
     // the label's name inside an IP. This code relies on the following assumption:
@@ -89,7 +87,7 @@ const std::vector<instruction>& assembly_scanner::get_fragments() {
             string label(curr_line.substr(0, i));
 
             [[maybe_unused]] auto _0 = label_names.insert(label);
-            auto [_, inserted] = m_label_locations.insert({ label, m_fragments->size() });
+            auto [_, inserted] = m_label_locations.insert({ label, m_instructions.size() });
 
             if (!inserted) {
                 cerr << "Label '" << label << "' appears twice" << endl;
@@ -125,7 +123,7 @@ const std::vector<instruction>& assembly_scanner::get_fragments() {
                 instruction::argument arg;
                 string label(curr_line.substr(label_start));
                 arg.next = { SIZE_C(0), label_to_fake_location(label) };
-                m_fragments->push_back({ opcode, arg });
+                m_instructions.push_back({ opcode, arg });
                 m_slices.push_back(curr_line);
                 break;
             }
@@ -134,8 +132,8 @@ const std::vector<instruction>& assembly_scanner::get_fragments() {
                 size_t label_start = curr_line.find_first_not_of(WHITESPACE, 3);
                 instruction::argument arg;
                 string label(curr_line.substr(label_start));
-                arg.choice = { { SIZE_C(0), m_fragments->size() + 1 }, { SIZE_C(0), label_to_fake_location(label) } };
-                m_fragments->push_back({ opcode, arg });
+                arg.choice = { { SIZE_C(0), m_instructions.size() + 1 }, { SIZE_C(0), label_to_fake_location(label) } };
+                m_instructions.push_back({ opcode, arg });
                 m_slices.push_back(curr_line);
                 break;
             }
@@ -188,19 +186,27 @@ const std::vector<instruction>& assembly_scanner::get_fragments() {
 
                 instruction::argument arg;
                 arg.number = arg_value;
-                m_fragments->push_back({ opcode, arg });
+                m_instructions.push_back({ opcode, arg });
                 m_slices.push_back(curr_line);
                 break;
             }
             default:
-                m_fragments->push_back({ opcode, instruction::argument() });
+                m_instructions.push_back({ opcode, instruction::argument() });
                 m_slices.push_back(curr_line);
                 break;
         }
     }
 
+    if (!m_instructions.empty()) {
+        const auto& last_instr = m_instructions.back();
+        if (!(last_instr.is_exit() || last_instr.m_op == instruction::operation::JMP)) {
+            cerr << "Program does not end in an exit instruction or loop" << endl;
+            exit(EXIT_FAILURE);
+        }
+    }
+
     // Second pass
-    for (auto& instr : *m_fragments) {
+    for (auto& instr : m_instructions) {
         if (instr.m_op == instruction::operation::JMP) {
             fake_location_to_real(instr.m_arg.next);
         } else if (instr.m_op == instruction::operation::TSP || instr.m_op == instruction::operation::BNG) {
@@ -208,7 +214,7 @@ const std::vector<instruction>& assembly_scanner::get_fragments() {
         }
     }
 
-    return *m_fragments;
+    return m_instructions;
 }
 
 void assembly_scanner::advance(IP& ip, std::function<bool()> go_left) {
diff --git a/src/assembly_scanner.hh b/src/assembly_scanner.hh
index 0e3e336..430b41d 100644
--- a/src/assembly_scanner.hh
+++ b/src/assembly_scanner.hh
@@ -10,24 +10,24 @@ public:
     using IP = size_t;
 
     inline assembly_scanner(const std::string& program) :
-        m_label_locations(), m_program(program), m_fragments(std::nullopt), m_slices{} {}
+        m_label_locations(), m_program(program), m_instructions{}, m_slices{} {}
 
-    const std::vector<instruction>& get_fragments();
+    const std::vector<instruction>& get_instructions();
 
     void advance(IP& ip, std::function<bool()> go_left);
 
     inline std::string raw_at(const IP& ip) {
-        [[maybe_unused]] auto _ = get_fragments();
+        [[maybe_unused]] auto _ = get_instructions();
         return std::string(m_slices[ip]);
     }
     inline std::pair<size_t, size_t> get_coords(const IP& ip) const { return { SIZE_C(0), ip }; }
-    inline instruction at(const IP& ip) { return get_fragments()[ip]; }
+    inline instruction at(const IP& ip) { return get_instructions()[ip]; }
 private:
     void fake_location_to_real(std::pair<size_t, size_t>& p) const;
     static instruction::operation opcode_for_name(const std::string_view& name) noexcept;
 
     std::unordered_map<std::string, IP> m_label_locations;
     std::string m_program;
-    std::optional<std::vector<instruction>> m_fragments;
+    std::vector<instruction> m_instructions;
     std::vector<std::string_view> m_slices;
 };
diff --git a/src/main.cpp b/src/main.cpp
index 01dfbf2..34dc508 100644
--- a/src/main.cpp
+++ b/src/main.cpp
@@ -20,7 +20,7 @@ inline void execute(const std::string& prg, flags f) {
 
     if (f.assembly) {
         assembly_scanner as(prg);
-        if (as.get_fragments().size() == 0) {
+        if (as.get_instructions().size() == 0) {
             empty_program();
         }
         interpreter i(as, f);