diff --git a/libsrc/apple2/ser/a2.ssc.s b/libsrc/apple2/ser/a2.ssc.s
index 1dbf5f3a4..7705f0933 100644
--- a/libsrc/apple2/ser/a2.ssc.s
+++ b/libsrc/apple2/ser/a2.ssc.s
@@ -328,20 +328,21 @@ SER_PUT:
 
         ; Try to send
         ldy     SendFreeCnt
-        iny                     ; Y = $FF?
+        cpy     #$FF            ; Nothing to flush
         beq     :+
         pha
         lda     #$00            ; TryHard = false
         jsr     TryToSend
         pla
 
-        ; Put byte into send buffer & send
-:       ldy     SendFreeCnt
+        ; Reload SendFreeCnt after TryToSend
+        ldy     SendFreeCnt
         bne     :+
         lda     #SER_ERR_OVERFLOW
         ldx     #0 ; return value is char
         rts
 
+        ; Put byte into send buffer & send
 :       ldy     SendTail
         sta     SendBuf,y
         inc     SendTail
diff --git a/libsrc/atmos/ser/atmos-acia.s b/libsrc/atmos/ser/atmos-acia.s
index 774a337bd..c918fe995 100644
--- a/libsrc/atmos/ser/atmos-acia.s
+++ b/libsrc/atmos/ser/atmos-acia.s
@@ -269,20 +269,21 @@ SER_GET:
 SER_PUT:
         ; Try to send
         ldy     SendFreeCnt
-        iny                     ; Y = $FF?
+        cpy     #$FF            ; Nothing to flush
         beq     :+
         pha
         lda     #$00            ; TryHard = false
         jsr     TryToSend
         pla
 
-        ; Put byte into send buffer & send
-:       ldy     SendFreeCnt
+        ; Reload SendFreeCnt after TryToSend
+        ldy     SendFreeCnt
         bne     :+
         lda     #SER_ERR_OVERFLOW
         ldx     #0 ; return value is char
         rts
 
+        ; Put byte into send buffer & send
 :       ldy     SendTail
         sta     SendBuf,y
         inc     SendTail
diff --git a/libsrc/c128/ser/c128-swlink.s b/libsrc/c128/ser/c128-swlink.s
index 57b5ea3b2..a0fc43050 100644
--- a/libsrc/c128/ser/c128-swlink.s
+++ b/libsrc/c128/ser/c128-swlink.s
@@ -362,21 +362,23 @@ SER_PUT:
 ; Try to send
 
         ldx     SendFreeCnt
-        inx                             ; X = $ff?
+        cpx     #$FF                   ; Nothing to flush
         beq     @L2
         pha
         lda     #$00
         jsr     TryToSend
         pla
 
-; Put byte into send buffer & send
+; Reload SendFreeCnt after TryToSend
 
-@L2:    ldx     SendFreeCnt
-        bne     @L3
+        ldx     SendFreeCnt
+        bne     @L2
         lda     #SER_ERR_OVERFLOW       ; X is already zero
         rts
 
-@L3:    ldx     SendTail
+; Put byte into send buffer & send
+
+@L2:    ldx     SendTail
         sta     SendBuf,x
         inc     SendTail
         dec     SendFreeCnt
diff --git a/libsrc/c64/ser/c64-swlink.s b/libsrc/c64/ser/c64-swlink.s
index 8c8b8bf39..c2934e669 100644
--- a/libsrc/c64/ser/c64-swlink.s
+++ b/libsrc/c64/ser/c64-swlink.s
@@ -336,21 +336,23 @@ SER_PUT:
 ; Try to send
 
         ldx     SendFreeCnt
-        inx                             ; X = $ff?
+        cpx     #$FF                   ; Nothing to flush
         beq     @L2
         pha
         lda     #$00
         jsr     TryToSend
         pla
 
-; Put byte into send buffer & send
+; Reload SendFreeCnt after TryToSend
 
-@L2:    ldx     SendFreeCnt
-        bne     @L3
+        ldx     SendFreeCnt
+        bne     @L2
         lda     #SER_ERR_OVERFLOW      ; X is already zero
         rts
 
-@L3:    ldx     SendTail
+; Put byte into send buffer & send
+
+@L2:    ldx     SendTail
         sta     SendBuf,x
         inc     SendTail
         dec     SendFreeCnt
diff --git a/libsrc/cbm510/ser/cbm510-std.s b/libsrc/cbm510/ser/cbm510-std.s
index 34fe02d0f..633a392c7 100644
--- a/libsrc/cbm510/ser/cbm510-std.s
+++ b/libsrc/cbm510/ser/cbm510-std.s
@@ -292,21 +292,23 @@ SER_PUT:
 ; Try to send
 
         ldx     SendFreeCnt
-        inx                             ; X = $ff?
+        cpx     #$FF                   ; Nothing to flush
         beq     @L2
         pha
         lda     #$00
         jsr     TryToSend
         pla
 
-; Put byte into send buffer & send
+; Reload SendFreeCnt after TryToSend
 
-@L2:    ldx     SendFreeCnt
-        bne     @L3
+        ldx     SendFreeCnt
+        bne     @L2
         lda     #SER_ERR_OVERFLOW      ; X is already zero
         rts
 
-@L3:    ldx     SendTail
+; Put byte into send buffer & send
+
+@L2:    ldx     SendTail
         sta     SendBuf,x
         inc     SendTail
         dec     SendFreeCnt
diff --git a/libsrc/cbm610/ser/cbm610-std.s b/libsrc/cbm610/ser/cbm610-std.s
index c241d5908..1216e3794 100644
--- a/libsrc/cbm610/ser/cbm610-std.s
+++ b/libsrc/cbm610/ser/cbm610-std.s
@@ -293,21 +293,23 @@ SER_PUT:
 ; Try to send
 
         ldx     SendFreeCnt
-        inx                             ; X = $ff?
+        cpx     #$ff                   ; Nothing to flush
         beq     @L2
         pha
         lda     #$00
         jsr     TryToSend
         pla
 
-; Put byte into send buffer & send
+; Reload SendFreeCnt after TryToSend
 
-@L2:    ldx     SendFreeCnt
-        bne     @L3
+        ldx     SendFreeCnt
+        bne     @L2
         lda     #SER_ERR_OVERFLOW      ; X is already zero
         rts
 
-@L3:    ldx     SendTail
+; Put byte into send buffer & send
+
+@L2:    ldx     SendTail
         sta     SendBuf,x
         inc     SendTail
         dec     SendFreeCnt
diff --git a/libsrc/plus4/ser/plus4-stdser.s b/libsrc/plus4/ser/plus4-stdser.s
index 5c4c550e6..d1d84267f 100644
--- a/libsrc/plus4/ser/plus4-stdser.s
+++ b/libsrc/plus4/ser/plus4-stdser.s
@@ -300,21 +300,23 @@ SER_PUT:
 ; Try to send
 
         ldx     SendFreeCnt
-        inx                             ; X = $ff?
+        cpx     #$ff                   ; Nothing to flush
         beq     @L2
         pha
         lda     #$00
         jsr     TryToSend
         pla
 
-; Put byte into send buffer & send
+; Reload SendFreeCnt after TryToSend
 
-@L2:    ldx     SendFreeCnt
-        bne     @L3
+        ldx     SendFreeCnt
+        bne     @L2
         lda     #SER_ERR_OVERFLOW      ; X is already zero
         rts
 
-@L3:    ldx     SendTail
+; Put byte into send buffer & send
+
+@L2:    ldx     SendTail
         sta     SendBuf,x
         inc     SendTail
         dec     SendFreeCnt