diff --git a/src/common.h b/src/common.h
index c07252f..09a1d32 100644
--- a/src/common.h
+++ b/src/common.h
@@ -36,6 +36,8 @@ typedef int32_t int32;
 	SDL_LogWarn(SDL_LOG_CATEGORY_APPLICATION, "%s:%d: " fmt, __func__, __LINE__, ##__VA_ARGS__)
 #define NOTICE SDL_Log
 
+[[noreturn]] void sys_error(const char* format, ...);
+
 #ifndef WIN32
 
 #define _MAX_PATH PATH_MAX
diff --git a/src/sdlmain.cpp b/src/sdlmain.cpp
index 321b6d5..196af19 100644
--- a/src/sdlmain.cpp
+++ b/src/sdlmain.cpp
@@ -119,6 +119,16 @@ int main(int argc, char *argv[])
     return exit_code;
 }
 
+[[noreturn]] void sys_error(const char* format, ...) {
+	char buf[512];
+	va_list args;
+	va_start(args, format);
+	vsnprintf(buf, sizeof buf, format, args);
+	SDL_LogError(SDL_LOG_CATEGORY_APPLICATION, "Fatal Error: %s", buf);
+	SDL_ShowSimpleMessageBox(SDL_MESSAGEBOX_ERROR, "system3", buf, g_window);
+	exit(1);
+}
+
 #ifdef __EMSCRIPTEN__
 
 extern "C"
diff --git a/src/sys/ags.cpp b/src/sys/ags.cpp
index 91ec1e8..8993be5 100644
--- a/src/sys/ags.cpp
+++ b/src/sys/ags.cpp
@@ -100,11 +100,11 @@ AGS::AGS(NACT* parent, const Config& config) : nact(parent), dirty(false)
 	if (!config.font_file.empty()) {
 		rw_font = open_file(config.font_file.c_str());
 		if (!rw_font)
-			parent->fatal("Cannot open font file %s", config.font_file.c_str());
+			sys_error("Cannot open font file %s", config.font_file.c_str());
 	} else {
 		rw_font = open_resource(FONT_RESOURCE_NAME, "fonts");
 		if (!rw_font)
-			parent->fatal("Cannot open default font");
+			sys_error("Cannot open default font");
 	}
 	hFont16 = TTF_OpenFontRW(rw_font, 0, 16);
 	SDL_RWseek(rw_font, 0, SEEK_SET);
@@ -116,7 +116,7 @@ AGS::AGS(NACT* parent, const Config& config) : nact(parent), dirty(false)
 	SDL_RWseek(rw_font, 0, SEEK_SET);
 	hFont64 = TTF_OpenFontRW(rw_font, 0, 64);
 	if (!hFont16 || !hFont24 || !hFont32 || !hFont48 || !hFont64) {
-		parent->fatal("TTF_OpenFontRW failed: %s", TTF_GetError());
+		sys_error("TTF_OpenFontRW failed: %s", TTF_GetError());
 	}
 	if (config.no_antialias)
 		ags_setAntialiasedStringMode(0);
diff --git a/src/sys/nact.cpp b/src/sys/nact.cpp
index 7367c69..68c71ea 100644
--- a/src/sys/nact.cpp
+++ b/src/sys/nact.cpp
@@ -37,7 +37,7 @@ NACT::NACT(int sys_ver, uint32 crc32_a, uint32 crc32_b, const Config& config)
 		char string[MAX_CAPTION];
 		fio->ag00_gets(string, MAX_CAPTION);
 		if (sscanf_s(string, "%d,%d,%d,%d", &d0, &d1, &d2, &d3) != 4)
-			fatal("AG00.DAT: parse error");
+			sys_error("AG00.DAT: parse error");
 		for(int i = 0; i < d1; i++) {
 			// 動詞の読み込み
 			fio->ag00_gets(string, MAX_CAPTION);
@@ -151,7 +151,7 @@ EMSCRIPTEN_KEEPALIVE  // Prevent inlining, because this function is listed in AS
 void NACT::execute()
 {
 	if (!sco.is_addr_valid()) {
-		fatal("Scenario error: invalid address %d:0x%x", sco.page(), sco.addr());
+		sys_error("Scenario error: invalid address %d:0x%x", sco.page(), sco.addr());
 		return;
 	}
 
@@ -293,9 +293,9 @@ void NACT::execute()
 				sco.ungetd();
 				message(0);
 			} else if (cmd >= 0x20 && cmd < 0x7f) {
-				fatal("Unknown Command: '%c' at page = %d, addr = %d", cmd, sco.page(), prev_addr);
+				sys_error("Unknown Command: '%c' at page = %d, addr = %d", cmd, sco.page(), prev_addr);
 			} else {
-				fatal("Unknown Command: %02x at page = %d, addr = %d", cmd, sco.page(), prev_addr);
+				sys_error("Unknown Command: %02x at page = %d, addr = %d", cmd, sco.page(), prev_addr);
 			}
 			break;
 	}
@@ -502,16 +502,6 @@ void NACT::select_cursor()
 	ags->select_cursor();
 }
 
-[[noreturn]] void NACT::fatal(const char* format, ...) {
-	char buf[512];
-	va_list args;
-	va_start(args, format);
-	vsnprintf(buf, sizeof buf, format, args);
-	SDL_LogError(SDL_LOG_CATEGORY_APPLICATION, "Fatal Error: %s", buf);
-	SDL_ShowSimpleMessageBox(SDL_MESSAGEBOX_ERROR, "system3", buf, g_window);
-	exit(1);
-}
-
 NACT* NACT::create(const Config& config) {
 	uint32 crc32_a = NACT::calc_crc32("ADISK.DAT", config.game_id);
 	uint32 crc32_b = NACT::calc_crc32("BDISK.DAT", config.game_id);
diff --git a/src/sys/nact.h b/src/sys/nact.h
index 74f4e5f..01ae4e2 100644
--- a/src/sys/nact.h
+++ b/src/sys/nact.h
@@ -275,8 +275,6 @@ public:
 
 	int get_scenario_page() const { return sco.page(); }
 
-	[[noreturn]] void fatal(const char* msg, ...);
-
 private:
 	void pump_events();
 	bool handle_platform_event(const SDL_Event& e);
diff --git a/src/sys/nact_sys1.cpp b/src/sys/nact_sys1.cpp
index ea4c279..e80999e 100644
--- a/src/sys/nact_sys1.cpp
+++ b/src/sys/nact_sys1.cpp
@@ -222,9 +222,9 @@ void NACT_Sys1::cmd_branch()
 				sco.ungetd();
 				sco.skip(encoding->mblen(sco.ptr()));
 			} else if (cmd >= 0x20 && cmd < 0x7f) {
-				fatal("Unknown Command: '%c' at page = %d, addr = %d", cmd, sco.page(), prev_addr);
+				sys_error("Unknown Command: '%c' at page = %d, addr = %d", cmd, sco.page(), prev_addr);
 			} else {
-				fatal("Unknown Command: %02x at page = %d, addr = %d", cmd, sco.page(), prev_addr);
+				sys_error("Unknown Command: %02x at page = %d, addr = %d", cmd, sco.page(), prev_addr);
 			}
 		}
 	}
@@ -605,19 +605,19 @@ void NACT_Sys1::cmd_a()
 void NACT_Sys1::cmd_b()
 {
 	// 未使用
-	fatal("Unknown Command: 'B' at page = %d, addr = %d", sco.page(), prev_addr);
+	sys_error("Unknown Command: 'B' at page = %d, addr = %d", sco.page(), prev_addr);
 }
 
 void NACT_Sys1::cmd_d()
 {
 	// 未使用
-	fatal("Unknown Command: 'D' at page = %d, addr = %d", sco.page(), prev_addr);
+	sys_error("Unknown Command: 'D' at page = %d, addr = %d", sco.page(), prev_addr);
 }
 
 void NACT_Sys1::cmd_e()
 {
 	// 未使用
-	fatal("Unknown Command: 'E' at page = %d, addr = %d", sco.page(), prev_addr);
+	sys_error("Unknown Command: 'E' at page = %d, addr = %d", sco.page(), prev_addr);
 }
 
 void NACT_Sys1::cmd_f()
@@ -655,25 +655,25 @@ void NACT_Sys1::cmd_g()
 void NACT_Sys1::cmd_h()
 {
 	// 未使用
-	fatal("Unknown Command: 'H' at page = %d, addr = %d", sco.page(), prev_addr);
+	sys_error("Unknown Command: 'H' at page = %d, addr = %d", sco.page(), prev_addr);
 }
 
 void NACT_Sys1::cmd_i()
 {
 	// 未使用
-	fatal("Unknown Command: 'I' at page = %d, addr = %d", sco.page(), prev_addr);
+	sys_error("Unknown Command: 'I' at page = %d, addr = %d", sco.page(), prev_addr);
 }
 
 void NACT_Sys1::cmd_j()
 {
 	// 未使用
-	fatal("Unknown Command: 'J' at page = %d, addr = %d", sco.page(), prev_addr);
+	sys_error("Unknown Command: 'J' at page = %d, addr = %d", sco.page(), prev_addr);
 }
 
 void NACT_Sys1::cmd_k()
 {
 	// 未使用
-	fatal("Unknown Command: 'K' at page = %d, addr = %d", sco.page(), prev_addr);
+	sys_error("Unknown Command: 'K' at page = %d, addr = %d", sco.page(), prev_addr);
 }
 
 void NACT_Sys1::cmd_l()
@@ -777,19 +777,19 @@ void NACT_Sys1::cmd_l()
 void NACT_Sys1::cmd_m()
 {
 	// 未使用
-	fatal("Unknown Command: 'M' at page = %d, addr = %d", sco.page(), prev_addr);
+	sys_error("Unknown Command: 'M' at page = %d, addr = %d", sco.page(), prev_addr);
 }
 
 void NACT_Sys1::cmd_n()
 {
 	// 未使用
-	fatal("Unknown Command: 'N' at page = %d, addr = %d", sco.page(), prev_addr);
+	sys_error("Unknown Command: 'N' at page = %d, addr = %d", sco.page(), prev_addr);
 }
 
 void NACT_Sys1::cmd_o()
 {
 	// 未使用
-	fatal("Unknown Command: 'O' at page = %d, addr = %d", sco.page(), prev_addr);
+	sys_error("Unknown Command: 'O' at page = %d, addr = %d", sco.page(), prev_addr);
 }
 
 void NACT_Sys1::cmd_p()
@@ -925,7 +925,7 @@ void NACT_Sys1::cmd_s()
 void NACT_Sys1::cmd_t()
 {
 	// 未使用
-	fatal("Unknown Command: 'T' at page = %d, addr = %d", sco.page(), prev_addr);
+	sys_error("Unknown Command: 'T' at page = %d, addr = %d", sco.page(), prev_addr);
 }
 
 void NACT_Sys1::cmd_u()
@@ -949,13 +949,13 @@ void NACT_Sys1::cmd_u()
 void NACT_Sys1::cmd_v()
 {
 	// 未使用
-	fatal("Unknown Command: 'V' at page = %d, addr = %d", sco.page(), prev_addr);
+	sys_error("Unknown Command: 'V' at page = %d, addr = %d", sco.page(), prev_addr);
 }
 
 void NACT_Sys1::cmd_w()
 {
 	// 未使用
-	fatal("Unknown Command: 'W' at page = %d, addr = %d", sco.page(), prev_addr);
+	sys_error("Unknown Command: 'W' at page = %d, addr = %d", sco.page(), prev_addr);
 }
 
 void NACT_Sys1::cmd_x()
@@ -1353,7 +1353,7 @@ uint16 NACT_Sys1::cali()
 		}
 	}
 	if (!ok) {
-		fatal("cali: invalid expression at %d:%04x", sco.page(), sco.addr());
+		sys_error("cali: invalid expression at %d:%04x", sco.page(), sco.addr());
 	}
 	return (uint16)(cali[1] & 0xffff);
 }
@@ -1368,10 +1368,10 @@ uint16 NACT_Sys1::cali2()
 	} else if(0xc0 <= dat && dat <= 0xff) {
 		val = ((dat & 0x3f) << 8) | sco.getd();
 	} else {
-		fatal("cali2: invalid expression at %d:%04x", sco.page(), sco.addr());
+		sys_error("cali2: invalid expression at %d:%04x", sco.page(), sco.addr());
 	}
 	if (sco.getd() != 0x7f) {
-		fatal("cali2: invalid expression at %d:%04x", sco.page(), sco.addr());
+		sys_error("cali2: invalid expression at %d:%04x", sco.page(), sco.addr());
 	}
 	return val;
 }
diff --git a/src/sys/nact_sys2.cpp b/src/sys/nact_sys2.cpp
index 859f6df..348e693 100644
--- a/src/sys/nact_sys2.cpp
+++ b/src/sys/nact_sys2.cpp
@@ -260,9 +260,9 @@ void NACT_Sys2::cmd_branch()
 				sco.ungetd();
 				sco.skip(encoding->mblen(sco.ptr()));
 			} else if (cmd >= 0x20 && cmd < 0x7f) {
-				fatal("Unknown Command: '%c' at page = %d, addr = %d", cmd, sco.page(), prev_addr);
+				sys_error("Unknown Command: '%c' at page = %d, addr = %d", cmd, sco.page(), prev_addr);
 			} else {
-				fatal("Unknown Command: %02x at page = %d, addr = %d", cmd, sco.page(), prev_addr);
+				sys_error("Unknown Command: %02x at page = %d, addr = %d", cmd, sco.page(), prev_addr);
 			}
 		}
 	}
@@ -1327,7 +1327,7 @@ uint16 NACT_Sys2::cali()
 		}
 	}
 	if (!ok) {
-		fatal("cali: invalid expression at %d:%04x", sco.page(), sco.addr());
+		sys_error("cali: invalid expression at %d:%04x", sco.page(), sco.addr());
 	}
 	return (uint16)(cali[1] & 0xffff);
 }
@@ -1342,10 +1342,10 @@ uint16 NACT_Sys2::cali2()
 	} else if(0xc0 <= dat && dat <= 0xff) {
 		val = ((dat & 0x3f) << 8) | sco.getd();
 	} else {
-		fatal("cali2: invalid expression at %d:%04x", sco.page(), sco.addr());
+		sys_error("cali2: invalid expression at %d:%04x", sco.page(), sco.addr());
 	}
 	if (sco.getd() != 0x7f) {
-		fatal("cali2: invalid expression at %d:%04x", sco.page(), sco.addr());
+		sys_error("cali2: invalid expression at %d:%04x", sco.page(), sco.addr());
 	}
 	return val;
 }
diff --git a/src/sys/nact_sys3.cpp b/src/sys/nact_sys3.cpp
index 2285f03..07716b8 100644
--- a/src/sys/nact_sys3.cpp
+++ b/src/sys/nact_sys3.cpp
@@ -386,7 +386,7 @@ void NACT_Sys3::cmd_b()
 void NACT_Sys3::cmd_d()
 {
 	// 未使用
-	fatal("Unknown Command: 'D' at page = %d, addr = %d", sco.page(), prev_addr);
+	sys_error("Unknown Command: 'D' at page = %d, addr = %d", sco.page(), prev_addr);
 }
 
 void NACT_Sys3::cmd_e()
@@ -1488,7 +1488,7 @@ uint16 NACT_Sys3::cali()
 		}
 	}
 	if (!ok) {
-		fatal("cali: invalid expression at %d:%04x", sco.page(), sco.addr());
+		sys_error("cali: invalid expression at %d:%04x", sco.page(), sco.addr());
 	}
 	return (uint16)(cali[1] & 0xffff);
 }
@@ -1503,10 +1503,10 @@ uint16 NACT_Sys3::cali2()
 	} else if(0xc0 <= dat && dat <= 0xff) {
 		val = ((dat & 0x3f) << 8) | sco.getd();
 	} else {
-		fatal("cali2: invalid expression at %d:%04x", sco.page(), sco.addr());
+		sys_error("cali2: invalid expression at %d:%04x", sco.page(), sco.addr());
 	}
 	if (sco.getd() != 0x7f) {
-		fatal("cali2: invalid expression at %d:%04x", sco.page(), sco.addr());
+		sys_error("cali2: invalid expression at %d:%04x", sco.page(), sco.addr());
 	}
 	return val;
 }
diff --git a/src/sys/scenario.cpp b/src/sys/scenario.cpp
index 73d2b42..9a70aae 100644
--- a/src/sys/scenario.cpp
+++ b/src/sys/scenario.cpp
@@ -1,5 +1,6 @@
 #include "scenario.h"
 #include <string.h>
+#include "common.h"
 #include "encoding.h"
 
 void Scenario::skip_string(Encoding *enc, uint8_t terminator)
@@ -20,10 +21,10 @@ void Scenario::get_syseng_string(char* buf, int size, Encoding *enc, uint8_t ter
 		if (c != '\\')
 			ungetd();
 		int len = enc->mblen(ptr());
-		if (i + len < size - 1) {
-			memcpy(&buf[i], ptr(), len);
-			i += len;
-		}
+		if (i + len >= size)
+			sys_error("String buffer overrun at %d:0x%x", page(), start_addr);
+		memcpy(&buf[i], ptr(), len);
+		i += len;
 		skip(len);
 	}
 	buf[i] = '\0';
diff --git a/src/win/mako.cpp b/src/win/mako.cpp
index ca72cd5..8015789 100644
--- a/src/win/mako.cpp
+++ b/src/win/mako.cpp
@@ -52,7 +52,7 @@ class MCIThread {
 public:
 	MCIThread(NACT* nact, HWND hwnd_notify) : hwnd_notify(hwnd_notify) {
 		if (!_beginthreadex(NULL, 0, &MCIThread::run, this, 0, &thread_id))
-			nact->fatal("Cannot create thread: %s", strerror(errno));
+			sys_error("Cannot create thread: %s", strerror(errno));
 	}
 
 	bool post_message(UINT msg, WPARAM wparam, LPARAM lparam) {
@@ -235,7 +235,7 @@ MAKO::MAKO(NACT* parent, const Config& config) :
 	SDL_SysWMinfo info;
 	SDL_VERSION(&info.version);
 	if (!SDL_GetWindowWMInfo(g_window, &info))
-		parent->fatal("SDL_GetWindowWMInfo failed: %s", SDL_GetError());
+		sys_error("SDL_GetWindowWMInfo failed: %s", SDL_GetError());
 	mci_thread = new MCIThread(parent, info.info.win.window);
 
 	midi = std::make_unique<MAKOMidi>(config.midi_device);