diff --git a/asm/ffi.py b/asm/ffi.py
index 3442171..54a47dc 100644
--- a/asm/ffi.py
+++ b/asm/ffi.py
@@ -89,7 +89,7 @@ class Environment:
 			return creole.from_2c(self.cenv.reg[reg])
 		else:
 			return self.cenv.reg[reg]
-	def getstk(self, stk):
+	def getstk(self, stk, signed=False):
 		""" Get the value at the stack position.
 
 		:param reg: Register number.
@@ -98,7 +98,16 @@ class Environment:
 		"""
 		if stk >= self.cenv.stklen or stk < 0:
 			raise StackOverflowError(r)
-		return creole.from_2c(self.cenv.stk[stk])
+		if signed:
+			return creole.from_2c(self.cenv.stk[stk])
+		else:
+			return self.cenv.stk[stk]
+
+	def pop(self):
+		if stk == 0:
+			return None
+		stk = stk - 1
+		return self.cenv.stk[stk]
 
 	def __init__(self, prog=None, reglen=32, lablen=32, stklen=4096, prglen=4096):
 		cenv = CEnv()
diff --git a/asm/test.py b/asm/test.py
index 19778b5..d50b555 100644
--- a/asm/test.py
+++ b/asm/test.py
@@ -434,5 +434,22 @@ class ProgramTest(unittest.TestCase):
 		self.range_test(0x7FFFF00, 0x8000000, sgn=True)
 		self.range_test(-100, 0, sgn=True)
 
+class SCEnv(ffi.Environment):
+	def syscall(self, s):
+		self.s = s.value
+	def __init__(self, *args, **kwargs):
+		super().__init__(*args, **kwargs)
+
+class ProgramTest(unittest.TestCase):
+	def range_test(self, st, en, sgn=False):
+		for i in range(st, en):
+			p = Program()
+			p.parse_asm_line(f"sys {i}")
+			ex = SCEnv(p())
+			self.assertEqual(ex(), ffi.RunRet.STOP)
+			self.assertEqual(ex.s, i)
+	def test_syscall_imm(self):
+		self.range_test(0, 1000)
+
 if __name__ == "__main__":
 	unittest.main()