diff --git a/libsrc/osic1p/_scrsize.s b/libsrc/osic1p/_scrsize.s
index 337fe1ee7..b0241c547 100644
--- a/libsrc/osic1p/_scrsize.s
+++ b/libsrc/osic1p/_scrsize.s
@@ -13,7 +13,7 @@
         .include        "osic1p.inc"
 
 .proc   screensize
-        ldx     #(SCR_LINELEN + 1)
-        ldy     #(SCR_HEIGHT + 1)
+        ldx     #SCR_LINELEN
+        ldy     #SCR_HEIGHT
         rts
 .endproc
diff --git a/libsrc/osic1p/cputc.s b/libsrc/osic1p/cputc.s
index 47969df15..9e6ae3253 100644
--- a/libsrc/osic1p/cputc.s
+++ b/libsrc/osic1p/cputc.s
@@ -35,7 +35,7 @@ cputdirect:
 ; Advance cursor position
 
 advance:
-        cpy     #SCR_LINELEN    ; xsize-1
+        cpy     #(SCR_LINELEN - 1)
         bne     L3
         jsr     newline         ; new line
         ldy     #$FF            ; + cr
diff --git a/libsrc/osic1p/osic1p.inc b/libsrc/osic1p/osic1p.inc
index e95db637e..f49bc122b 100644
--- a/libsrc/osic1p/osic1p.inc
+++ b/libsrc/osic1p/osic1p.inc
@@ -6,5 +6,5 @@ KBD             := $DF00        ; Polled keyboard register
 
 ; Other definitions
 VIDEORAMSIZE    = $0400         ; Size of C1P video RAM (1 kB)
-SCR_LINELEN     = $18           ; screen width - 1
-SCR_HEIGHT      = $18           ; screen height - 1
+SCR_LINELEN     = $19           ; screen width
+SCR_HEIGHT      = $19           ; screen height