diff --git a/src/config.c b/src/config.c
index 41551d94a5..c82a4cb8b1 100644
--- a/src/config.c
+++ b/src/config.c
@@ -125,7 +125,7 @@ void config_load()
 {
 	FILE *fp=NULL;
 
-	char* path = get_file_path(PATH_ID_GAMECFG);
+	const char *path = get_file_path(PATH_ID_GAMECFG);
 
 	fp = fopen(path, "rb");
 
diff --git a/src/rct2.c b/src/rct2.c
index 5f18db7805..559fced6bf 100644
--- a/src/rct2.c
+++ b/src/rct2.c
@@ -232,9 +232,16 @@ void subsitute_path(char *dest, const char *path, const char *filename)
 // rct2: 0x00674B42
 void rct2_startup_checks()
 {
-	// check if game is already running
+	// Check if game is already running
+	if (check_mutex())
+	{
+		RCT2_ERROR("Game is already running");
+		RCT2_CALLPROC_X(0x006E3838, 0x343, 0xB2B, 0, 0, 0, 0, 0); // exit_with_error
+	}
 
-	RCT2_CALLPROC_EBPSAFE(0x00674C0B);
+	// Check data files
+	check_file_paths();
+	check_files_integrity();
 }
 
 void rct2_update()
@@ -305,6 +312,99 @@ void check_cmdline_arg()
 	}
 }
 
+// rct2: 0x00407DB0
+int check_mutex()
+{
+	const char * const mutex_name = "RollerCoaster Tycoon 2_GSKMUTEX"; // rct2 @ 0x009AAC3D + 0x009A8B50
+
+	HANDLE mutex = OpenMutex(MUTEX_ALL_ACCESS, FALSE, mutex_name);
+
+	if (mutex != NULL)
+	{
+		// Already running
+		CloseHandle(mutex);
+		return 1;
+	}
+
+	HANDLE status = CreateMutex(NULL, FALSE, mutex_name);
+	return 0;
+}
+
+// rct2: 0x00674C95
+void check_file_paths()
+{
+	for (int pathId = 0; pathId < PATH_ID_END; pathId += 1)
+	{
+		check_file_path(pathId);
+	}
+}
+
+// rct2: 0x00674CA5
+void check_file_path(int pathId)
+{
+	const char * path = get_file_path(pathId);
+	HANDLE file = CreateFile(path, FILE_GENERIC_READ, FILE_SHARE_READ, NULL, OPEN_EXISTING, FILE_ATTRIBUTE_NORMAL | FILE_FLAG_RANDOM_ACCESS, NULL);
+
+	switch (pathId)
+	{
+	case PATH_ID_GAMECFG:
+	case PATH_ID_SCORES:
+		// Do nothing; these will be created later if they do not exist yet
+		break;
+
+	case PATH_ID_CUSTOM1:
+		if (file != INVALID_HANDLE_VALUE)
+			RCT2_GLOBAL(0x009AF164, unsigned int) = SetFilePointer(file, 0, 0, FILE_END); // Store file size in music_custom1_size @ 0x009AF164
+		break;
+
+	case PATH_ID_CUSTOM2:
+		if (file != INVALID_HANDLE_VALUE)
+			RCT2_GLOBAL(0x009AF16E, unsigned int) = SetFilePointer(file, 0, 0, FILE_END); // Store file size in music_custom2_size @ 0x009AF16E
+		break;
+
+	default:
+		if (file == INVALID_HANDLE_VALUE) {
+			// A data file is missing from the installation directory. The original implementation
+			// asks for a CD-ROM path at this point and stores it in cdrom_path @ 0x9AA318.
+			// The file_on_cdrom[pathId] @ 0x009AA0B flag is set to 1 as well.
+			// For PATH_ID_SIXFLAGS_MAGICMOUNTAIN and PATH_ID_SIXFLAGS_BUILDYOUROWN,
+			// the original implementation always assumes they are stored on CD-ROM.
+			// This has been removed for now for the sake of simplicity and could be added
+			// later in a more convenient way using the INI file.
+			RCT2_ERROR("Could not find file %s", path);
+			RCT2_CALLPROC_X(0x006E3838, 0x343, 0x337, 0, 0, 0, 0, 0); // exit_with_error
+		}
+		break;
+	}
+
+	if (file != INVALID_HANDLE_VALUE)
+		CloseHandle(file);
+}
+
+// rct2: 0x00674C0B
+void check_files_integrity()
+{
+	int i = 0;
+	while (files_to_check[i].pathId != PATH_ID_END)
+	{
+		WIN32_FIND_DATA find_data;
+		const char * path = get_file_path(files_to_check[i].pathId);
+		HANDLE file = FindFirstFile(path, &find_data);
+
+		if (file == INVALID_HANDLE_VALUE || find_data.nFileSizeLow != files_to_check[i].fileSize)
+		{
+			if (file != INVALID_HANDLE_VALUE)
+				FindClose(file);
+			RCT2_ERROR("Integrity check failed for %s", path);
+			RCT2_CALLPROC_X(0x006E3838, 0x343, 0x337, 0, 0, 0, 0, 0); // exit_with_error
+		}
+
+		FindClose(file);
+
+		i += 1;
+	}
+}
+
 void rct2_update_2()
 {
 	int tick, tick2;
@@ -346,13 +446,39 @@ void rct2_endupdate()
  * 
  *  rct2: 0x00674E6C
  */
-char *get_file_path(int pathId)
+const char *get_file_path(int pathId)
 {
-	int eax, ebx, ecx, edx, esi, edi, ebp;
+	static char path[MAX_PATH]; // get_file_path_buffer @ 0x009E3605
 
-	ebx = pathId;
-	RCT2_CALLFUNC_X(0x00674E6C, &eax, &ebx, &ecx, &edx, &esi, &edi, &ebp);
-	return (char*)ebx;
+	// The original implementation checks if the file is on CD-ROM here (file_on_cdrom[pathId] @ 0x009AA0B1).
+	// If so, the CD-ROM path (cdrom_path @ 0x9AA318) is used instead. This has been removed for now for
+	// the sake of simplicity.
+	strcpy(path, gGeneral_config.game_path);
+
+	// Make sure base path is terminated with a slash
+	if (strlen(path) == 0 || path[strlen(path) - 1] != '\\')
+	{
+		if (strlen(path) >= MAX_PATH - 1)
+		{
+			RCT2_ERROR("Path for %s too long", file_paths[pathId]);
+			path[0] = '\0';
+			return path;
+		}
+
+		strcat(path, "\\");
+	}
+
+	// Concatenate file path
+	if (strlen(path) + strlen(file_paths[pathId]) > MAX_PATH)
+	{
+		RCT2_ERROR("Path for %s too long", file_paths[pathId]);
+		path[0] = '\0';
+		return path;
+	}
+
+	strcat(path, file_paths[pathId]);
+
+	return path;
 }
 
 /**
diff --git a/src/rct2.h b/src/rct2.h
index f5b765b206..dcdb81bcc0 100644
--- a/src/rct2.h
+++ b/src/rct2.h
@@ -157,13 +157,116 @@ enum {
 	PATH_ID_CSS43,
 	PATH_ID_CSS44,
 	PATH_ID_CSS45,
-	PATH_ID_CSS46
+	PATH_ID_CSS46,
+	PATH_ID_END
+};
 
+// rct2 @ 0x0097F67C
+static const char * const file_paths[] =
+{
+	"Data\\G1.DAT",
+	"Data\\PLUGIN.DAT",
+	"Data\\CSS1.DAT",
+	"Data\\CSS2.DAT",
+	"Data\\CSS4.DAT",
+	"Data\\CSS5.DAT",
+	"Data\\CSS6.DAT",
+	"Data\\CSS7.DAT",
+	"Data\\CSS8.DAT",
+	"Data\\CSS9.DAT",
+	"Data\\CSS10.DAT",
+	"Data\\CSS11.DAT",
+	"Data\\CSS12.DAT",
+	"Data\\CSS13.DAT",
+	"Data\\CSS14.DAT",
+	"Data\\CSS15.DAT",
+	"Data\\CSS16.DAT",
+	"Data\\CSS3.DAT",
+	"Data\\GAME.CFG",
+	"Data\\TUT640A.DAT",
+	"Data\\TUT640B.DAT",
+	"Data\\TUT640C.DAT",
+	"Data\\TUT800A.DAT",
+	"Data\\TUT800B.DAT",
+	"Data\\TUT800C.DAT",
+	"Data\\KANJI.DAT",
+	"Data\\CSS17.DAT",
+	"Data\\CSS18.DAT",
+	"Data\\CSS19.DAT",
+	"Data\\CSS20.DAT",
+	"Data\\CSS21.DAT",
+	"Data\\CSS22.DAT",
+	"Saved Games\\scores.DAT",
+	"Data\\CSS23.DAT",
+	"Data\\CSS24.DAT",
+	"Data\\CSS25.DAT",
+	"Data\\CSS26.DAT",
+	"Data\\CSS27.DAT",
+	"Data\\CSS28.DAT",
+	"Data\\CSS29.DAT",
+	"Data\\CSS30.DAT",
+	"Data\\CSS31.DAT",
+	"Data\\CSS32.DAT",
+	"Data\\CSS33.DAT",
+	"Data\\CSS34.DAT",
+	"Data\\CSS35.DAT",
+	"Data\\CSS36.DAT",
+	"Data\\CSS37.DAT",
+	"Data\\CSS38.DAT",
+	"Data\\CUSTOM1.WAV",
+	"Data\\CUSTOM2.WAV",
+	"Data\\CSS39.DAT",
+	"Data\\CSS40.DAT",
+	"Tracks\\Tracks.IDX",
+	"Data\\CSS41.DAT",
+	"Scenarios\\Six Flags Magic Mountain.SC6",
+	"Scenarios\\Build your own Six Flags Park.SC6",
+	"Data\\CSS42.DAT",
+	"Data\\CSS43.DAT",
+	"Data\\CSS44.DAT",
+	"Data\\CSS45.DAT",
+	"Data\\CSS46.DAT"
+};
+
+// Files to check (rct2 @ 0x0097FB5A)
+static const struct file_to_check
+{
+	int pathId; // ID of file
+	unsigned int fileSize; // Expected size in bytes
+} files_to_check[] = {
+	{ PATH_ID_CSS18,  8429568 },
+	{ PATH_ID_CSS19, 10143784 },
+	{ PATH_ID_CSS20, 12271656 },
+	{ PATH_ID_CSS21,  9680968 },
+	{ PATH_ID_CSS22, 10062056 },
+	{ PATH_ID_CSS23, 11067432 },
+	{ PATH_ID_CSS24, 12427456 },
+	{ PATH_ID_CSS25, 15181512 },
+	{ PATH_ID_CSS26, 10694816 },
+	{ PATH_ID_CSS27, 10421232 },
+	{ PATH_ID_CSS28, 13118376 },
+	{ PATH_ID_CSS29, 15310892 },
+	{ PATH_ID_CSS30, 10215464 },
+	{ PATH_ID_CSS31, 11510316 },
+	{ PATH_ID_CSS32, 11771944 },
+	{ PATH_ID_CSS33, 10759724 },
+	{ PATH_ID_CSS34, 14030716 },
+	{ PATH_ID_CSS35, 11642576 },
+	{ PATH_ID_CSS36,  8953764 },
+	{ PATH_ID_CSS37, 13303852 },
+	{ PATH_ID_CSS38, 10093888 },
+	{ PATH_ID_CSS39,  7531564 },
+	{ PATH_ID_CSS40,  5291306 },
+	{ PATH_ID_END,          0 }
 };
 
 void rct2_endupdate();
 void subsitute_path(char *dest, const char *path, const char *filename);
-char *get_file_path(int pathId);
+int check_mutex();
+void check_file_paths();
+void check_file_path(int pathId);
+void check_files_integrity();
+const char *get_file_path(int pathId);
 void get_system_info();
 void get_system_time();
 void get_local_time();