diff --git a/src/sys/scenario.cpp b/src/sys/scenario.cpp
index f91eb3b..c78d1da 100644
--- a/src/sys/scenario.cpp
+++ b/src/sys/scenario.cpp
@@ -1,4 +1,5 @@
 #include "scenario.h"
+#include <algorithm>
 #include <string.h>
 #include "common.h"
 #include "encoding.h"
@@ -44,35 +45,92 @@ void Scenario::get_syseng_string(char* buf, int size, Encoding *enc, uint8_t ter
 void Scenario::label_call(int label)
 {
 	if (label == 0) {
-		if (label_stack.empty()) {
+		// Return
+		auto it = std::find_if(call_stack.rbegin(), call_stack.rend(),
+			[](const StackFrame& frame) { return !frame.is_page_call; });
+		if (it == call_stack.rend()) {
 			WARNING("Label stack underflow");
 			return;
 		}
-		jump_to(label_stack.back());
-		label_stack.pop_back();
+		if (it != call_stack.rbegin()) {
+			WARNING("Return from non-top label call");
+		}
+		if (it->page != page_) {
+			sys_error("Illegal label return at %d:%04x", page_, cmd_addr_);
+		}
+		jump_to(it->addr);
+		call_stack.erase(std::next(it).base());
 	} else {
-		label_stack.push_back(addr_);
+		call_stack.emplace_back(false, page_, addr_);
 		jump_to(label);
 	}
 }
 
+size_t Scenario::label_stack_size() const
+{
+	return std::count_if(call_stack.begin(), call_stack.end(),
+		[](const StackFrame& frame) { return !frame.is_page_call; });
+}
+
+void Scenario::label_stack_pop()
+{
+	auto it = std::find_if(call_stack.rbegin(), call_stack.rend(),
+		[](const StackFrame& frame) { return !frame.is_page_call; });
+	if (it == call_stack.rend())
+		return;
+	call_stack.erase(std::next(it).base());
+}
+
+void Scenario::label_stack_clear()
+{
+	call_stack.erase(std::remove_if(call_stack.begin(), call_stack.end(),
+		[](const StackFrame& frame) { return !frame.is_page_call; }), call_stack.end());
+}
+
 void Scenario::page_call(int target_page)
 {
 	if (target_page == 0) {
-		if (page_stack.empty()) {
+		// Return
+		auto it = std::find_if(call_stack.rbegin(), call_stack.rend(),
+			[](const StackFrame& frame) { return frame.is_page_call; });
+		if (it == call_stack.rend()) {
 			WARNING("Page stack underflow");
 			return;
 		}
-		auto& pair = page_stack.back();
-		page_jump(pair.first, pair.second);
-		page_stack.pop_back();
+		if (it != call_stack.rbegin()) {
+			WARNING("Return from non-top page call");
+		}
+		page_jump(it->page, it->addr);
+		call_stack.erase(std::next(it).base());
 	} else {
-		page_stack.emplace_back(page_, addr_);
+		call_stack.emplace_back(true, page_, addr_);
 		page_jump(target_page, 2);
 	}
 }
 
-[[noreturn]] void Scenario::unknown_command(uint8_t cmd) {
+size_t Scenario::page_stack_size() const
+{
+	return std::count_if(call_stack.begin(), call_stack.end(),
+		[](const StackFrame& frame) { return frame.is_page_call; });
+}
+
+void Scenario::page_stack_pop()
+{
+	auto it = std::find_if(call_stack.rbegin(), call_stack.rend(),
+		[](const StackFrame& frame) { return frame.is_page_call; });
+	if (it == call_stack.rend())
+		return;
+	call_stack.erase(std::next(it).base());
+}
+
+void Scenario::page_stack_clear()
+{
+	call_stack.erase(std::remove_if(call_stack.begin(), call_stack.end(),
+		[](const StackFrame& frame) { return frame.is_page_call; }), call_stack.end());
+}
+
+[[noreturn]] void Scenario::unknown_command(uint8_t cmd)
+{
 	if (cmd >= 0x20 && cmd < 0x7f) {
 		sys_error("Unknown Command: '%c' at %d:%04x", cmd, page_, cmd_addr_);
 	} else {
diff --git a/src/sys/scenario.h b/src/sys/scenario.h
index 6d85a3b..f73e5ce 100644
--- a/src/sys/scenario.h
+++ b/src/sys/scenario.h
@@ -40,25 +40,35 @@ public:
 	void get_syseng_string(char* buf, int size, Encoding *enc, uint8_t terminator);
 
 	void label_call(int label);
-	size_t label_stack_size() const { return label_stack.size(); }
-	void label_stack_pop() { label_stack.pop_back(); }
-	void label_stack_clear() { label_stack.clear(); }
+	size_t label_stack_size() const;
+	void label_stack_pop();
+	void label_stack_clear();
 
 	void page_call(int page);
-	size_t page_stack_size() const { return page_stack.size(); }
-	void page_stack_pop() { page_stack.pop_back(); }
-	void page_stack_clear() { page_stack.clear(); }
+	size_t page_stack_size() const;
+	void page_stack_pop();
+	void page_stack_clear();
 
 	[[noreturn]] void unknown_command(uint8_t cmd);
 
+	struct StackFrame {
+		bool is_page_call;
+		uint8_t page;
+		uint16_t addr;
+
+		StackFrame(bool is_page_call, uint8_t page, uint16_t addr)
+			: is_page_call(is_page_call), page(page), addr(addr) {}
+	};
+	const std::vector<StackFrame>& get_call_stack() const { return call_stack; }
+	int write_instruction(int page, int addr, uint8_t op);
+
 private:
 	Dri adisk;
 	std::vector<uint8_t> data_;
 	int page_;
 	int addr_;
 	int cmd_addr_;
-	std::vector<int> label_stack;
-	std::vector<std::pair<int, int>> page_stack;
+	std::vector<StackFrame> call_stack;
 };
 
 #endif // _SCENARIO_H_