diff --git a/src/main/scala/millfork/assembly/mos/AssemblyLine.scala b/src/main/scala/millfork/assembly/mos/AssemblyLine.scala
index ca320be1..41222882 100644
--- a/src/main/scala/millfork/assembly/mos/AssemblyLine.scala
+++ b/src/main/scala/millfork/assembly/mos/AssemblyLine.scala
@@ -494,12 +494,18 @@ object AssemblyLine {
   def absoluteX(opcode: Opcode.Value, thing: ThingInMemory, offset: Int = 0) =
     AssemblyLine(opcode, AddrMode.AbsoluteX, thing.toAddress + offset)
 
+  def indexedY(opcode: Opcode.Value, addr: Int) =
+    AssemblyLine(opcode, AddrMode.IndexedY, NumericConstant(addr & 0xff, 1))
+
   def indexedY(opcode: Opcode.Value, addr: Constant) =
     AssemblyLine(opcode, AddrMode.IndexedY, addr)
 
   def indexedY(opcode: Opcode.Value, thing: ThingInMemory, offset: Int = 0) =
     AssemblyLine(opcode, AddrMode.IndexedY, thing.toAddress + offset)
 
+  def indexedSY(opcode: Opcode.Value, offset: Int = 0) =
+    AssemblyLine(opcode, AddrMode.IndexedSY, NumericConstant(offset & 0xff, 1))
+
   def stackRelative(opcode: Opcode.Value, addr: Int) =
     AssemblyLine(opcode, AddrMode.Stack, NumericConstant(addr & 0xff, 1))
 }
diff --git a/src/main/scala/millfork/assembly/mos/opt/ChangeIndexRegisterOptimization.scala b/src/main/scala/millfork/assembly/mos/opt/ChangeIndexRegisterOptimization.scala
index 0d5a33b8..935bb406 100644
--- a/src/main/scala/millfork/assembly/mos/opt/ChangeIndexRegisterOptimization.scala
+++ b/src/main/scala/millfork/assembly/mos/opt/ChangeIndexRegisterOptimization.scala
@@ -38,14 +38,14 @@ class ChangeIndexRegisterOptimization(preferX2Y: Boolean) extends AssemblyOptimi
         OpcodeClasses.ReadsYAlways(l.opcode) ||
         OpcodeClasses.ChangesX(l.opcode) ||
         OpcodeClasses.ChangesY(l.opcode) ||
-        Set(AbsoluteX, AbsoluteY, ZeroPageY, ZeroPageX, IndexedX, IndexedY)(l.addrMode)
+        Set(AbsoluteX, AbsoluteY, ZeroPageY, ZeroPageX, IndexedX, IndexedY, LongIndexedY, IndexedSY)(l.addrMode)
     )
     val usesY = code.exists(l =>
       OpcodeClasses.ReadsXAlways(l.opcode) ||
         OpcodeClasses.ReadsYAlways(l.opcode) ||
         OpcodeClasses.ChangesX(l.opcode) ||
         OpcodeClasses.ChangesY(l.opcode) ||
-        Set(AbsoluteX, AbsoluteY, ZeroPageY, ZeroPageX, IndexedX, IndexedY)(l.addrMode)
+        Set(AbsoluteX, AbsoluteY, ZeroPageY, ZeroPageX, IndexedX, IndexedY, LongIndexedY, IndexedSY)(l.addrMode)
     )
     if (!usesX && !usesY) {
       return code
@@ -109,6 +109,7 @@ class ChangeIndexRegisterOptimization(preferX2Y: Boolean) extends AssemblyOptimi
     case AssemblyLine0(_, ZeroPageY, _) :: xs if loaded != Some(Y) => false
     case AssemblyLine0(_, IndexedY, _) :: xs if dir == Y2X || loaded != Some(Y) => false
     case AssemblyLine0(_, LongIndexedY, _) :: xs if dir == Y2X || loaded != Some(Y) => false
+    case AssemblyLine0(_, IndexedSY, _) :: xs if dir == Y2X || loaded != Some(Y) => false
     case AssemblyLine0(_, AbsoluteX, _) :: xs if loaded != Some(X) => false
     case AssemblyLine0(_, LongAbsoluteX, _) :: xs if loaded != Some(X) => false
     case AssemblyLine0(_, ZeroPageX, _) :: xs if loaded != Some(X) => false
@@ -225,6 +226,8 @@ class ChangeIndexRegisterOptimization(preferX2Y: Boolean) extends AssemblyOptimi
     case (x@AssemblyLine0(_, AbsoluteY, _)) :: xs => x.copy(addrMode = AbsoluteX) :: switchY2X(xs)
     case (x@AssemblyLine0(_, ZeroPageY, _)) :: xs => x.copy(addrMode = ZeroPageX) :: switchY2X(xs)
     case AssemblyLine0(_, IndexedY, _) :: xs => log.fatal("Unexpected IndexedY")
+    case AssemblyLine0(_, LongIndexedY, _) :: xs => log.fatal("Unexpected LongIndexedY")
+    case AssemblyLine0(_, IndexedSY, _) :: xs => log.fatal("Unexpected IndexedSY")
 
     case x::xs => x :: switchY2X(xs)
     case Nil => Nil
diff --git a/src/main/scala/millfork/output/MosAssembler.scala b/src/main/scala/millfork/output/MosAssembler.scala
index f4245df0..1d313655 100644
--- a/src/main/scala/millfork/output/MosAssembler.scala
+++ b/src/main/scala/millfork/output/MosAssembler.scala
@@ -50,7 +50,7 @@ class MosAssembler(program: Program,
         writeByte(bank, index, MosAssembler.opcodeFor(op, Relative, options))
         writeByte(bank, index + 1, AssertByte(param - (index + 2)))
         index + 2
-      case AssemblyLine0(op, am@(Immediate | ZeroPage | ZeroPageX | ZeroPageY | IndexedY | IndexedX | IndexedZ | LongIndexedY | LongIndexedZ | Stack), param) =>
+      case AssemblyLine0(op, am@(Immediate | ZeroPage | ZeroPageX | ZeroPageY | IndexedY | IndexedX | IndexedZ | IndexedSY | LongIndexedY | LongIndexedZ | Stack), param) =>
         writeByte(bank, index, MosAssembler.opcodeFor(op, am, options))
         writeByte(bank, index + 1, param)
         index + 2
diff --git a/src/test/resources/cpu.js b/src/test/resources/cpu.js
index 3a612b6e..be399f64 100644
--- a/src/test/resources/cpu.js
+++ b/src/test/resources/cpu.js
@@ -2898,6 +2898,7 @@ var STA_stack_relative_indirect_indexed_y= {
   execute:function(cpu, bytes) {
     cpu.cycle_count+=7;
 
+    // TODO: fixes below are not well-tested!
     if(cpu.p.e) {
       var location_loc = 0x100 | ((cpu.r.s + bytes[0]) & 0xff),
           low_byte =  cpu.mmu.read_byte(location_loc),
@@ -2907,41 +2908,16 @@ var STA_stack_relative_indirect_indexed_y= {
       } else {
         high_byte = cpu.mmu.read_byte(location_loc+1);
       }
-      var absolute_location = ((high_byte<<8)|low_byte)+cpu.r.y,
-          b;
-      if(absolute_location>=0x10000) {
-        b = cpu.mmu.read_byte_long(absolute_location, cpu.r.dbr+1);
-      } else {
-        b = cpu.mmu.read_byte(absolute_location);
-      }
-      cpu.mmu.store_byte(b, cpu.r.a);
+      var absolute_location = ((high_byte<<8)|low_byte)+cpu.r.y;
+      cpu.mmu.store_byte(absolute_location, cpu.r.a);
     } else {
       var location_loc = cpu.r.s + bytes[0],
           absolute_location = cpu.mmu.read_word(location_loc)+cpu.r.y;
       if(cpu.p.m) {
-        var b;
-        if(absolute_location>=0x10000) {
-          b = cpu.mmu.read_byte_long(absolute_location, cpu.r.dbr+1);
-        } else {
-          b = cpu.mmu.read_byte(absolute_location);
-        }
-        cpu.mmu.store_byte(b, cpu.r.a);
+        cpu.mmu.store_byte(absolute_location, cpu.r.a);
       } else {
         cpu.cycle_count++;
-
-        var low_byte, high_byte;
-        if(absolute_location>=0x10000) {
-          low_byte = cpu.mmu.read_byte_long(absolute_location, cpu.r.dbr+1);
-          high_byte = cpu.mmu.read_byte_long(absolute_location+1, cpu.r.dbr+1);
-        } else {
-          low_byte = cpu.mmu.read_byte(absolute_location);
-          if(absolute_location===0xffff) {
-            high_byte = cpu.mmu.read_byte_long(0, cpu.r.dbr+1);
-          } else {
-            high_byte = cpu.mmu.read_byte(absolute_location);
-          }
-        }
-        cpu.mmu.store_word((high_byte<<8)|low_byte, cpu.r.a);
+        cpu.mmu.store_word(absolute_location, cpu.r.a);
       }
     }
   }