diff --git a/codeGenCpu6502/src/prog8/codegen/cpu6502/AsmGen.kt b/codeGenCpu6502/src/prog8/codegen/cpu6502/AsmGen.kt
index d85bca51a..b146fe260 100644
--- a/codeGenCpu6502/src/prog8/codegen/cpu6502/AsmGen.kt
+++ b/codeGenCpu6502/src/prog8/codegen/cpu6502/AsmGen.kt
@@ -1707,7 +1707,13 @@ $repeatLabel    lda  $counterVar
         // sign extend signed byte in A to full word in AY
         when(valueDt) {
             DataType.UBYTE -> out("  ldy  #0")
-            DataType.BYTE -> out("  jsr  prog8_lib.sign_extend_AY_byte")
+            DataType.BYTE -> out("""
+                ldy  #0
+                cmp  #$80
+                bcc  +
+                dey
++
+            """)
             else -> throw AssemblyError("need byte type")
         }
     }
diff --git a/codeGenCpu6502/src/prog8/codegen/cpu6502/assignment/AugmentableAssignmentAsmGen.kt b/codeGenCpu6502/src/prog8/codegen/cpu6502/assignment/AugmentableAssignmentAsmGen.kt
index 59f47857b..faba060a4 100644
--- a/codeGenCpu6502/src/prog8/codegen/cpu6502/assignment/AugmentableAssignmentAsmGen.kt
+++ b/codeGenCpu6502/src/prog8/codegen/cpu6502/assignment/AugmentableAssignmentAsmGen.kt
@@ -1158,17 +1158,16 @@ internal class AugmentableAssignmentAsmGen(private val program: Program,
 +""")
                         else
                             asmgen.out("""
-                                ldy  #0
+                                ldy  #255
                                 lda  $otherName
                                 bpl  +
-                                dey     ; sign extend
-+                               sty  P8ZP_SCRATCH_B1
-                                lda  $name
+                                iny     ; sign extend
++                               eor  #255
                                 sec
-                                sbc  $otherName
+                                adc  $name
                                 sta  $name
-                                lda  $name+1
-                                sbc  P8ZP_SCRATCH_B1
+                                tya
+                                adc  $name+1
                                 sta  $name+1""")
                     }
                     "*" -> {
@@ -1446,29 +1445,28 @@ internal class AugmentableAssignmentAsmGen(private val program: Program,
                                 sta  $name+1""")
                     }
                     "-" -> {
-                        asmgen.assignExpressionToVariable(value, "P8ZP_SCRATCH_REG", valueDt, null)
+                        asmgen.assignExpressionToVariable(value, "P8ZP_SCRATCH_B1", valueDt, null)
                         if(valueDt==DataType.UBYTE)
                             asmgen.out("""
                                 lda  $name
                                 sec
-                                sbc  P8ZP_SCRATCH_REG
+                                sbc  P8ZP_SCRATCH_B1
                                 sta  $name
                                 bcs  +
                                 dec  $name+1
 +""")
                         else
                             asmgen.out("""
-                                ldy  #0
-                                lda  P8ZP_SCRATCH_REG
+                                ldy  #255
+                                lda  P8ZP_SCRATCH_B1
                                 bpl  +
-                                dey         ; sign extend
-+                               sty  P8ZP_SCRATCH_B1
-                                lda  $name
+                                iny         ; sign extend
++                               eor  #255
                                 sec
-                                sbc  P8ZP_SCRATCH_REG
+                                adc  $name
                                 sta  $name
-                                lda  $name+1
-                                sbc  P8ZP_SCRATCH_B1
+                                tya
+                                adc  $name+1
                                 sta  $name+1""")
                     }
                     "*" -> {
@@ -2105,40 +2103,38 @@ internal class AugmentableAssignmentAsmGen(private val program: Program,
                         when(target.register!!) { //P8ZP_SCRATCH_REG
                             RegisterOrPair.AX -> {
                                 asmgen.out("""
-                                    sta  P8ZP_SCRATCH_REG
-                                    stx  P8ZP_SCRATCH_REG+1
-                                    lda  #0
                                     sec
-                                    sbc  P8ZP_SCRATCH_REG
+                                    eor  #255
+                                    adc  #0
                                     pha
-                                    lda  #0
-                                    sbc  P8ZP_SCRATCH_REG+1
+                                    txa
+                                    eor  #255
+                                    adc  #0
                                     tax
                                     pla""")
                             }
                             RegisterOrPair.AY -> {
                                 asmgen.out("""
-                                    sta  P8ZP_SCRATCH_REG
-                                    sty  P8ZP_SCRATCH_REG+1
-                                    lda  #0
                                     sec
-                                    sbc  P8ZP_SCRATCH_REG
+                                    eor  #255
+                                    adc  #0
                                     pha
-                                    lda  #0
-                                    sbc  P8ZP_SCRATCH_REG+1
+                                    tya
+                                    eor  #255
+                                    adc  #0
                                     tay
                                     pla""")
                             }
                             RegisterOrPair.XY -> {
                                 asmgen.out("""
-                                    stx  P8ZP_SCRATCH_REG
-                                    sty  P8ZP_SCRATCH_REG+1
-                                    lda  #0
                                     sec
-                                    sbc  P8ZP_SCRATCH_REG
+                                    txa
+                                    eor  #255
+                                    adc  #0
                                     tax
-                                    lda  #0
-                                    sbc  P8ZP_SCRATCH_REG+1
+                                    tya
+                                    eor  #255
+                                    adc  #0
                                     tay""")
                             }
                             in Cx16VirtualRegisters -> throw AssemblyError("cx16 virtual regs should be variables, not real registers")
diff --git a/compiler/res/prog8lib/prog8_lib.asm b/compiler/res/prog8lib/prog8_lib.asm
index 3b87301af..ba0b1a501 100644
--- a/compiler/res/prog8lib/prog8_lib.asm
+++ b/compiler/res/prog8lib/prog8_lib.asm
@@ -1121,17 +1121,15 @@ strcmp_mem	.proc
 		;      Returns -1,0,1 in A, depeding on the ordering. Clobbers Y.
 		sta  P8ZP_SCRATCH_W1
 		sty  P8ZP_SCRATCH_W1+1
-_loop		ldy  #0
-		lda  (P8ZP_SCRATCH_W1),y
+		ldy  #0
+_loop		lda  (P8ZP_SCRATCH_W1),y
 		bne  +
 		lda  (P8ZP_SCRATCH_W2),y
 		bne  _return_minusone
 		beq  _return
-+		lda  (P8ZP_SCRATCH_W2),y
-		sec
-		sbc  (P8ZP_SCRATCH_W1),y
-		bmi  _return_one
-		bne  _return_minusone
++		cmp  (P8ZP_SCRATCH_W2),y
+		bcc  _return_minusone
+		bne  _return_one
 		inc  P8ZP_SCRATCH_W1
 		bne  +
 		inc  P8ZP_SCRATCH_W1+1
@@ -1158,20 +1156,6 @@ sign_extend_stack_byte	.proc
 		rts
 		.pend
 
-
-sign_extend_AY_byte	.proc
-	; -- sign extend the (signed) byte in AY to full 16 bits
-		pha
-		and  #$80
-		beq  +
-		ldy  #$ff
-		pla
-		rts
-+		ldy  #0
-		pla
-		rts
-		.pend
-
 strlen          .proc
         ; -- returns the number of bytes in the string in AY, in Y.
 		sta  P8ZP_SCRATCH_W1