diff --git a/compiler/res/prog8lib/conv.p8 b/compiler/res/prog8lib/conv.p8
index f9ed355bf..86a2752b6 100644
--- a/compiler/res/prog8lib/conv.p8
+++ b/compiler/res/prog8lib/conv.p8
@@ -12,14 +12,14 @@ conv {
 asmsub  str_ub0  (ubyte value @ A) clobbers(A,Y)  {
 	; ---- convert the ubyte in A in decimal string form, with left padding 0s (3 positions total)
 	%asm {{
-            phx
+            stx  P8ZP_SCRATCH_REG
             jsr  conv.ubyte2decimal
             sty  string_out
             sta  string_out+1
             stx  string_out+2
             lda  #0
             sta  string_out+3
-            plx
+            ldx  P8ZP_SCRATCH_REG
             rts
 	}}
 }
@@ -27,7 +27,7 @@ asmsub  str_ub0  (ubyte value @ A) clobbers(A,Y)  {
 asmsub  str_ub  (ubyte value @ A) clobbers(A,Y)  {
 	; ---- convert the ubyte in A in decimal string form, without left padding 0s
 	%asm {{
-		phx
+		stx  P8ZP_SCRATCH_REG
 		ldy  #0
 		sty  P8ZP_SCRATCH_B1
 		jsr  conv.ubyte2decimal
@@ -53,7 +53,7 @@ _output_byte_digits
                 iny
                 lda  #0
                 sta  string_out,y
-                plx
+                ldx  P8ZP_SCRATCH_REG
                 rts
 	}}
 }
@@ -61,7 +61,7 @@ _output_byte_digits
 asmsub  str_b  (byte value @ A) clobbers(A,Y)  {
 	; ---- convert the byte in A in decimal string form, without left padding 0s
 	%asm {{
-            phx
+            stx  P8ZP_SCRATCH_REG
             ldy  #0
             sty  P8ZP_SCRATCH_B1
             cmp  #0
@@ -149,7 +149,7 @@ asmsub  str_uwhex  (uword value @ AY) clobbers(A,Y)  {
 asmsub  str_uw0  (uword value @ AY) clobbers(A,Y)  {
 	; ---- convert the uword in A/Y in decimal string form, with left padding 0s (5 positions total)
 	%asm {{
-	    phx
+	    stx  P8ZP_SCRATCH_REG
 	    jsr  conv.uword2decimal
 	    ldy  #0
 -           lda  conv.uword2decimal.decTenThousands,y
@@ -157,7 +157,7 @@ asmsub  str_uw0  (uword value @ AY) clobbers(A,Y)  {
             beq  +
             iny
             bne  -
-+           plx
++           ldx  P8ZP_SCRATCH_REG
 	    rts
 	}}
 }
@@ -165,7 +165,7 @@ asmsub  str_uw0  (uword value @ AY) clobbers(A,Y)  {
 asmsub  str_uw  (uword value @ AY) clobbers(A,Y)  {
 	; ---- convert the uword in A/Y in decimal string form, without left padding 0s
 	%asm {{
-	    phx
+	    stx  P8ZP_SCRATCH_REG
 	    jsr  conv.uword2decimal
 	    ldx  #0
 _output_digits
@@ -183,7 +183,7 @@ _gotdigit   sta  string_out,x
             bne  _gotdigit
 _end        lda  #0
             sta  string_out,x
-            plx
+            ldx  P8ZP_SCRATCH_REG
             rts
 
 _allzero    lda  #'0'
@@ -198,7 +198,7 @@ asmsub  str_w  (word value @ AY) clobbers(A,Y)  {
 	%asm {{
 	    cpy  #0
 	    bpl  str_uw
-	    phx
+	    stx  P8ZP_SCRATCH_REG
 	    pha
 	    lda  #'-'
 	    sta  string_out