diff --git a/asm/creole.py b/asm/creole.py
index 2e323e4..3746003 100644
--- a/asm/creole.py
+++ b/asm/creole.py
@@ -11,6 +11,11 @@ def word_2c(w):
 def ti(w):
 	""" Explicitly transform integer into two's compliment representation. """
 	return w if w >= 0 else word_wc(-w)
+def from_2c(w):
+	""" Turn two's compliment word into Python integer. """
+	if (w >> 31) & 1 == 0:
+		return w
+	return -word_2c(w)
 
 class ArgType(Enum):
 	""" Class denoting the type of an argument to an instruction. """
@@ -86,9 +91,10 @@ class Instruction(Enum):
 	ADD = 3, ArgType.REG, ArgType.VAL, ArgType.VAL
 	MUL = 4, ArgType.REG, ArgType.VAL, ArgType.VAL
 	DIV = 5, ArgType.REG, ArgType.VAL, ArgType.VAL
-	JL = 6, ArgType.LAB, ArgType.VAL, ArgType.VAL
-	CLB = 7, ArgType.LAB
-	SYS = 8, ArgType.VAL
+	IDIV = 6, ArgType.REG, ArgType.VAL, ArgType.VAL
+	JL = 7, ArgType.LAB, ArgType.VAL, ArgType.VAL
+	CLB = 8, ArgType.LAB
+	SYS = 9, ArgType.VAL
 
 	def __init__(self, opcode, *args):
 		if opcode > 0x7F or opcode < 0:
diff --git a/asm/ffi.py b/asm/ffi.py
index a1907c6..4c1ca15 100644
--- a/asm/ffi.py
+++ b/asm/ffi.py
@@ -1,4 +1,5 @@
 from ctypes import *
+import creole
 from enum import Enum
 dll = CDLL("./libcreole.so")
 
@@ -24,6 +25,7 @@ class RunRet(Enum):
 	RUN_LABEL_OVERFLOW = 5
 	REGISTER_OVERFLOW = 6
 	UNKNOWN_OPCODE = 7
+	DIVIDE_BY_ZERO = 8
 
 	def is_halt(self):
 		return not (self == RunRet.CONTINUE or self == RunRet.SYSCALL)
@@ -59,8 +61,30 @@ class CEnv(Structure):
 		("prglen", c_size_t)
 	]
 
+class RegisterOverflowError(Exception):
+	def __init__(self, reg):
+		self.reg = reg
+class StackOverflowError(Exception):
+	def __init__(self, pos):
+		self.pos = pos
+class InvalidSyscallError(Exception):
+	def __init__(self, sc):
+		self.sc = sc
+class CompileError(Exception):
+	def __init__(self, r):
+		self.r = r
+
 class Environment:
-	def __init__(self, reglen=32, lablen=32, stklen=4096, prglen=4096):
+	def getreg(self, reg):
+		if reg >= self.cenv.reglen or reg < 0:
+			raise RegisterOverflowError(r)
+		return creole.from_2c(self.cenv.reg[reg])
+	def getstk(self, stk):
+		if stk >= self.cenv.stklen or stk < 0:
+			raise StackOverflowError(r)
+		return creole.from_2c(self.cenv.stk[stk])
+
+	def __init__(self, prog=None, reglen=32, lablen=32, stklen=4096, prglen=4096):
 		cenv = CEnv()
 		cenv.reglen = reglen
 		cenv.reg = (c_uint * reglen)()
@@ -78,6 +102,10 @@ class Environment:
 		cenv.prgend = 0
 
 		self.cenv = cenv
+		if prog is not None:
+			r = self.load(prog)
+			if r is not CompileRet.OK:
+				raise CompileError(r)
 
 	def restart(self):
 		self.cenv.stkptr = 0
@@ -91,7 +119,7 @@ class Environment:
 		return CompileRet(ret)
 
 	def syscall(self, sc):
-		pass
+		raise InvalidSyscallError(sc)
 	def __call__(self):
 		sc = c_size_t()
 		ret = RunRet.CONTINUE
diff --git a/asm/test.py b/asm/test.py
index 1f66a4a..1274d9c 100644
--- a/asm/test.py
+++ b/asm/test.py
@@ -56,10 +56,8 @@ class PushTest(unittest.TestCase):
 		p = Program()
 		p.parse_asm_line("PUSH r0")
 		p.parse_asm_line("PUSH 6")
-		b = p()
 
-		ex = ffi.Environment()
-		self.assertEqual(ex.load(b), ffi.CompileRet.OK)
+		ex = ffi.Environment(p())
 		self.assertEqual(ex.cenv.prgend, 2)
 
 		self.assertEqual(ex.cenv.prg[0].opcode, 1)
@@ -83,19 +81,17 @@ class PushTest(unittest.TestCase):
 		stklen = 40
 		for n in range(0,stklen):
 			p.parse_asm_line("PUSH 5")
-		ex = ffi.Environment(stklen=stklen)
-		self.assertEqual(ex.load(p()), ffi.CompileRet.OK)
+		ex = ffi.Environment(p(), stklen=stklen)
 		self.assertEqual(ex(), ffi.RunRet.STOP)
 		for n in range(0,stklen):
-			self.assertEqual(ex.cenv.stk[n], 5)
+			self.assertEqual(ex.getstk(n), 5)
 
 	def test_push_overflow(self):
 		p = Program()
 		stklen = 40
 		for n in range(0, stklen + 1):
 			p.parse_asm_line("PUSH 5")
-		ex = ffi.Environment(stklen=stklen)
-		self.assertEqual(ex.load(p()), ffi.CompileRet.OK)
+		ex = ffi.Environment(p(), stklen=stklen)
 		self.assertEqual(ex(), ffi.RunRet.STACK_OVERFLOW)
 
 class PopTest(unittest.TestCase):
@@ -104,8 +100,7 @@ class PopTest(unittest.TestCase):
 		p.parse_asm_line("pop r9")
 		b = p()
 		self.assertEqual(b, b'\x02\xC2\x89\x00')
-		ex = ffi.Environment()
-		self.assertEqual(ex.load(b), ffi.CompileRet.OK)
+		ex = ffi.Environment(b)
 		self.assertEqual(ex.cenv.prgend, 1)
 
 		self.assertEqual(ex.cenv.prg[0].opcode, 2)
@@ -152,8 +147,7 @@ class PopTest(unittest.TestCase):
 	def test_pop_underflow(self):
 		p = Program()
 		p.parse_asm_line("pop r0")
-		ex = ffi.Environment()
-		self.assertEqual(ex.load(p()), ffi.CompileRet.OK)
+		ex = ffi.Environment(p())
 		self.assertEqual(ex(), ffi.RunRet.STACK_UNDERFLOW)
 
 	def test_pop_underflow_2(self):
@@ -161,16 +155,14 @@ class PopTest(unittest.TestCase):
 		p.parse_asm_line("push 5")
 		p.parse_asm_line("pop r0")
 		p.parse_asm_line("pop r1")
-		ex = ffi.Environment()
-		self.assertEqual(ex.load(p()), ffi.CompileRet.OK)
+		ex = ffi.Environment(p())
 		self.assertEqual(ex(), ffi.RunRet.STACK_UNDERFLOW)
 
 class AddTest(unittest.TestCase):
 	def test_exec_add(self):
 		p = Program()
 		p.parse_asm_line("add r0 1 1")
-		ex = ffi.Environment()
-		self.assertEqual(ex.load(p()), ffi.CompileRet.OK)
+		ex = ffi.Environment(p())
 		self.assertEqual(ex(), ffi.RunRet.STOP)
 		self.assertEqual(ex.cenv.reg[0], 2)
 
@@ -179,11 +171,10 @@ class AddTest(unittest.TestCase):
 		p.parse_asm_line("add r0 10 20")
 		p.parse_asm_line("add r1 5 0")
 		p.parse_asm_line("add r1 r0 -40")
-		ex = ffi.Environment()
-		self.assertEqual(ex.load(p()), ffi.CompileRet.OK)
+		ex = ffi.Environment(p())
 		self.assertEqual(ex(), ffi.RunRet.STOP)
-		self.assertEqual(ex.cenv.reg[0], 30)
-		self.assertEqual(ex.cenv.reg[1], word_2c(10))
+		self.assertEqual(ex.getreg(0), 30)
+		self.assertEqual(ex.getreg(1), -10)
 
 	def test_exec_add_throw_imm(self):
 		p = Program()
@@ -216,20 +207,18 @@ class MulTest(unittest.TestCase):
 	def test_exec_mul_imm_imm(self):
 		p = Program()
 		p.parse_asm_line("mul r0 2 2")
-		ex = ffi.Environment()
-		self.assertEqual(ex.load(p()), ffi.CompileRet.OK)
+		ex = ffi.Environment(p())
 		self.assertEqual(ex(), ffi.RunRet.STOP)
-		self.assertEqual(ex.cenv.reg[0], 4)
+		self.assertEqual(ex.getreg(0), 4)
 
 	def test_exec_mul_imm_neg_imm(self):
 		p = Program()
 		p.parse_asm_line("mul r0 -5 5")
 		p.parse_asm_line("mul r1 r0 -5")
-		ex = ffi.Environment()
-		self.assertEqual(ex.load(p()), ffi.CompileRet.OK)
+		ex = ffi.Environment(p())
 		self.assertEqual(ex(), ffi.RunRet.STOP)
-		self.assertEqual(ex.cenv.reg[0], word_2c(25))
-		self.assertEqual(ex.cenv.reg[1], 125)
+		self.assertEqual(ex.getreg(0), -25)
+		self.assertEqual(ex.getreg(1), 125)
 
 	def test_exec_mul_throw_imm(self):
 		p = Program()
@@ -258,6 +247,68 @@ class MulTest(unittest.TestCase):
 		self.assertEqual(cm.exception.i, 2)
 		self.assertEqual(cm.exception.opcode, 4)
 
+class DivTest(unittest.TestCase):
+	def test_div(self):
+		p = Program()
+		p.parse_asm_line("div r0 8 4")
+		ex = ffi.Environment(p())
+		self.assertEqual(ex(), ffi.RunRet.STOP)
+		self.assertEqual(ex.getreg(0), 2)
+
+	def test_div_round_down(self):
+		p = Program()
+		p.parse_asm_line("div r0 8 10")
+		ex = ffi.Environment(p())
+		self.assertEqual(ex(), ffi.RunRet.STOP)
+
+	def test_div_by_zero(self):
+		p = Program()
+		p.parse_asm_line("div r0 8 0")
+		ex = ffi.Environment(p())
+		self.assertEqual(ex(), ffi.RunRet.DIVIDE_BY_ZERO)
+
+	def test_idiv_by_zero(self):
+		p = Program()
+		p.parse_asm_line("idiv r0 8 0")
+		ex = ffi.Environment(p())
+		self.assertEqual(ex(), ffi.RunRet.DIVIDE_BY_ZERO)
+
+	def test_div_neg(self):
+		p = Program()
+		p.parse_asm_line("idiv r0 16 -4")
+		p.parse_asm_line("idiv r1 r0 -4")
+		ex = ffi.Environment(p())
+		self.assertEqual(ex(), ffi.RunRet.STOP)
+		self.assertEqual(ex.getreg(0), -4)
+		self.assertEqual(ex.getreg(1), 1)
+
+	def test_exec_div_throw_imm(self):
+		p = Program()
+		with self.assertRaises(TypecheckException) as cm:
+			p.parse_asm_line("div 5 1 2")
+		self.assertEqual(cm.exception.argtype, ArgType.REG)
+		self.assertEqual(cm.exception.sarg, '5')
+		self.assertEqual(cm.exception.i, 0)
+		self.assertEqual(cm.exception.opcode, 5)
+
+	def test_exec_div_throw_lab_1(self):
+		p = Program()
+		with self.assertRaises(TypecheckException) as cm:
+			p.parse_asm_line("div r0 l123 456")
+		self.assertEqual(cm.exception.argtype, ArgType.VAL)
+		self.assertEqual(cm.exception.sarg, 'l123')
+		self.assertEqual(cm.exception.i, 1)
+		self.assertEqual(cm.exception.opcode, 5)
+
+	def test_exec_div_throw_lab_2(self):
+		p = Program()
+		with self.assertRaises(TypecheckException) as cm:
+			p.parse_asm_line("div r5 1919 l24")
+		self.assertEqual(cm.exception.argtype, ArgType.VAL)
+		self.assertEqual(cm.exception.sarg, 'l24')
+		self.assertEqual(cm.exception.i, 2)
+		self.assertEqual(cm.exception.opcode, 5)
+
 class ProgramTest(unittest.TestCase):
 	def test_exec_simple_reg(self):
 		p = Program()
@@ -268,8 +319,8 @@ class ProgramTest(unittest.TestCase):
 		ex = ffi.Environment()
 		self.assertEqual(ex.load(p()), ffi.CompileRet.OK)
 		self.assertEqual(ex(), ffi.RunRet.STOP)
-		self.assertEqual(ex.cenv.reg[0], 6)
-		self.assertEqual(ex.cenv.reg[1], 5)
+		self.assertEqual(ex.getreg(0), 6)
+		self.assertEqual(ex.getreg(1), 5)
 
 if __name__ == "__main__":
 	unittest.main()
diff --git a/creole.c b/creole.c
index 1fa6b11..8865939 100644
--- a/creole.c
+++ b/creole.c
@@ -35,6 +35,7 @@ static const struct {
 	defop(ADD, 3, TYPE_REG, TYPE_VAL, TYPE_VAL),
 	defop(MUL, 3, TYPE_REG, TYPE_VAL, TYPE_VAL),
 	defop(DIV, 3, TYPE_REG, TYPE_VAL, TYPE_VAL),
+	defop(IDIV, 3, TYPE_REG, TYPE_VAL, TYPE_VAL),
 	defop(JL, 3, TYPE_LAB, TYPE_VAL, TYPE_VAL),
 	defop(CLB, 1, TYPE_LAB, TYPE_NONE, TYPE_NONE),
 	defop(SYS, 1, TYPE_VAL, TYPE_NONE, TYPE_NONE)
@@ -323,8 +324,9 @@ creole_parse_line(struct creole_ins *ins, struct creole_reader *r)
 		return CREOLE_OPCODE_READ_ERROR;
 
 	ins->opcode = w.word;
-	if (w.word >= CREOLE_ARG_TYPE_LEN || w.len != 1)
+	if (w.word >= CREOLE_OPCODE_LEN || w.len != 1) {
 		return CREOLE_OPCODE_MALFORMED;
+	}
 
 	for (arg = 0; arg < opcode_info[ins->opcode].arglen; arg++) {
 		if (!decode_seq(r, &w))
@@ -542,8 +544,18 @@ enum creole_run_ret creole_step(struct creole_env *env, creole_word *sc)
 	case CREOLE_DIV:
 		check(read_val(env, ins, 1, &a1));
 		check(read_val(env, ins, 2, &a2));
+		if (a2 == 0)
+			return CREOLE_DIV_BY_ZERO;
 		check(creole_reg_write(env, ins->w[0], a1 / a2));
 		break;
+	case CREOLE_IDIV:
+		check(read_val(env, ins, 1, &a1));
+		check(read_val(env, ins, 2, &a2));
+		if (a2 == 0)
+			return CREOLE_DIV_BY_ZERO;
+		check(creole_reg_write(env, ins->w[0],
+		      (creole_signed)a1 / (creole_signed)a2));
+		break;
 	case CREOLE_JL:
 		check(read_val(env, ins, 1, &a1));
 		check(read_val(env, ins, 2, &a2));
diff --git a/creole.h b/creole.h
index ba10dda..0e84a72 100644
--- a/creole.h
+++ b/creole.h
@@ -7,11 +7,14 @@
 #ifndef CREOLE_WORD
 # define CREOLE_WORD unsigned int
 # define CREOLE_WORD_MAX UINT_MAX
+# define CREOLE_SIGNED_WORD int
+# define CREOLE_SIGNED_MAX INT_MAX
 #endif
 
 #define CREOLE_MAX_ARG 3
 
 typedef CREOLE_WORD creole_word;
+typedef CREOLE_SIGNED_WORD creole_signed;
 
 enum creole_opcode {
 	CREOLE_NOOP = 0,
@@ -20,9 +23,10 @@ enum creole_opcode {
 	CREOLE_ADD = 3,
 	CREOLE_MUL = 4,
 	CREOLE_DIV = 5,
-	CREOLE_JL = 6,
-	CREOLE_CLB = 7,
-	CREOLE_SYS = 8,
+	CREOLE_IDIV = 6,
+	CREOLE_JL = 7,
+	CREOLE_CLB = 8,
+	CREOLE_SYS = 9,
 	CREOLE_OPCODE_LEN
 };
 
@@ -56,6 +60,7 @@ enum creole_run_ret {
 	CREOLE_RUN_LABEL_OVERFLOW,
 	CREOLE_REGISTER_OVERFLOW,
 	CREOLE_STEP_UNKNOWN_OPCODE,
+	CREOLE_DIV_BY_ZERO,
 	CREOLE_RUN_RET_LEN
 };