diff --git a/src/arch/zx48k/optimizer/basicblock.py b/src/arch/zx48k/optimizer/basicblock.py
index eac5349c9..89ecf92db 100644
--- a/src/arch/zx48k/optimizer/basicblock.py
+++ b/src/arch/zx48k/optimizer/basicblock.py
@@ -12,6 +12,8 @@
 from .common import LABELS, JUMP_LABELS
 from .errors import OptimizerInvalidBasicBlockError, OptimizerError
 from .cpustate import CPUState
+from .patterns import RE_ID_OR_NUMBER
+
 from ..peephole import evaluator
 
 from . import helpers
@@ -377,6 +379,8 @@ def is_used(self, regs, i, top=None):
                 if helpers.idx_args(regs[0][1:-1]) else []
 
             rr = set(r16 + ix)
+            mem_vars = set([] if rr else RE_ID_OR_NUMBER.findall(regs[0]))
+
             for mem in self[i:top]:  # For memory accesses only mark as NOT uses if it's overwritten
                 if mem.inst == 'ld' and mem.opers[0] == regs[0]:
                     return False
@@ -387,6 +391,9 @@ def is_used(self, regs, i, top=None):
                 if rr and any(_ in r16 for _ in mem.destroys):  # (hl) :: inc hl / (ix + n) :: inc ix
                     return True
 
+                if mem.opers and mem_vars.intersection(RE_ID_OR_NUMBER.findall(mem.opers[-1])):
+                    return True
+
             return True
 
         regs = src.api.utils.flatten_list([helpers.single_registers(x) for x in regs])  # make a copy
diff --git a/src/arch/zx48k/optimizer/patterns.py b/src/arch/zx48k/optimizer/patterns.py
index ebb37127b..8055a3104 100644
--- a/src/arch/zx48k/optimizer/patterns.py
+++ b/src/arch/zx48k/optimizer/patterns.py
@@ -32,3 +32,6 @@
 
 # matches a pragma line
 RE_PRAGMA = re.compile(r'^#[ \t]?pragma[ \t]opt[ \t]')
+
+# matches an ID or a number
+RE_ID_OR_NUMBER = re.compile(r'[0-9]+|[a-zA-Z_][a-zA-Z_0-9]*')
diff --git a/src/arch/zx48k/peephole/evaluator.py b/src/arch/zx48k/peephole/evaluator.py
index f00778412..a3ca89b45 100644
--- a/src/arch/zx48k/peephole/evaluator.py
+++ b/src/arch/zx48k/peephole/evaluator.py
@@ -137,8 +137,8 @@ class Evaluator(object):
             || (or)
             +  (addition or concatenation for strings)
     """
-    UNARY = UNARY
-    BINARY = BINARY
+    UNARY = dict(UNARY)
+    BINARY = dict(BINARY)
 
     def __init__(self, expression, unary=None, binary=None):
         """ Initializes the object parsing the expression and preparing it for its (later)
diff --git a/tests/arch/zx48k/optimizer/test_basicblock.py b/tests/arch/zx48k/optimizer/test_basicblock.py
index 32be34c0b..6bced7ff3 100644
--- a/tests/arch/zx48k/optimizer/test_basicblock.py
+++ b/tests/arch/zx48k/optimizer/test_basicblock.py
@@ -3,14 +3,18 @@
 import unittest
 from src.arch.zx48k.optimizer import basicblock
 from src.arch.zx48k import optimizer
+from src.arch.zx48k.peephole import evaluator
 
 
 class TestBasicBlock(unittest.TestCase):
     """ Tests basic blocks implementation
     """
-    def setUp(self):
+    def setUp(self) -> None:
         self.blk = basicblock.BasicBlock([])
 
+    def tearDown(self) -> None:
+        evaluator.Evaluator.UNARY = dict(evaluator.UNARY)
+
     def test_block_partition_jp(self):
         code = """
         nop
@@ -157,3 +161,11 @@ def test_basic_block_clean_ld_hl(self):
         self.blk.code = [x for x in code.split('\n') if x.strip()]
         self.assertEqual(1, len(self.blk))
         self.assertEqual(['ld hl, (30000)'], self.blk.code)
+
+    def test_mempos_requires(self):
+        code = """
+        ld hl, (_k - 1)
+        ld (_k), a
+        """
+        self.blk.code = [x for x in code.split('\n') if x.strip()]
+        self.assertTrue(self.blk.is_used(['(_k)'], 0))
diff --git a/tests/functional/opt4_due_0.asm b/tests/functional/opt4_due_0.asm
new file mode 100644
index 000000000..7ea4e4285
--- /dev/null
+++ b/tests/functional/opt4_due_0.asm
@@ -0,0 +1,51 @@
+	org 32768
+__START_PROGRAM:
+	di
+	push ix
+	push iy
+	exx
+	push hl
+	exx
+	ld hl, 0
+	add hl, sp
+	ld (__CALL_BACK__), hl
+	ei
+	jp __MAIN_PROGRAM__
+ZXBASIC_USER_DATA:
+	; Defines USER DATA Length in bytes
+ZXBASIC_USER_DATA_LEN EQU ZXBASIC_USER_DATA_END - ZXBASIC_USER_DATA
+	.__LABEL__.ZXBASIC_USER_DATA_LEN EQU ZXBASIC_USER_DATA_LEN
+	.__LABEL__.ZXBASIC_USER_DATA EQU ZXBASIC_USER_DATA
+_k:
+	DEFB 05h
+_n:
+	DEFB 00
+ZXBASIC_USER_DATA_END:
+__MAIN_PROGRAM__:
+	ld a, (_k)
+	xor 31
+	ld (_k), a
+	ld a, (_n)
+	add a, a
+	add a, a
+	add a, a
+	add a, a
+	add a, a
+	ld hl, (_k - 1)
+	or h
+	ld (_k), a
+	ld bc, 0
+__END_PROGRAM:
+	di
+	ld hl, (__CALL_BACK__)
+	ld sp, hl
+	exx
+	pop hl
+	pop iy
+	pop ix
+	exx
+	ei
+	ret
+__CALL_BACK__:
+	DEFW 0
+	END
diff --git a/tests/functional/opt4_due_0.bas b/tests/functional/opt4_due_0.bas
new file mode 100644
index 000000000..3b9ca53b7
--- /dev/null
+++ b/tests/functional/opt4_due_0.bas
@@ -0,0 +1,9 @@
+
+
+DIM k as UByte = 5
+DIM n as UByte
+
+k = k bXOR %11111
+k = (n << 5) bOR k
+
+