diff --git a/libsrc/agat/cputc.s b/libsrc/agat/cputc.s
index b82ce22e6..052c10da5 100644
--- a/libsrc/agat/cputc.s
+++ b/libsrc/agat/cputc.s
@@ -5,6 +5,8 @@
 ; void __fastcall__ cputcxy (unsigned char x, unsigned char y, char c);
 ; void __fastcall__ cputc (char c);
 ;
+; Important note: The implementation of cputs() relies on the cputc() function
+; not clobbering ptr1. Beware when rewriting or changing this function!
 
     .import     COUT
     .export     _cputcxy, _cputc, newline, putchar,putchardirect
diff --git a/libsrc/apple2/cputc.s b/libsrc/apple2/cputc.s
index 5c4bf192e..dc851e11b 100644
--- a/libsrc/apple2/cputc.s
+++ b/libsrc/apple2/cputc.s
@@ -4,6 +4,8 @@
 ; void __fastcall__ cputcxy (unsigned char x, unsigned char y, char c);
 ; void __fastcall__ cputc (char c);
 ;
+; Important note: The implementation of cputs() relies on the cputc() function
+; not clobbering ptr1. Beware when rewriting or changing this function!
 
         .constructor    initconio
         .export         _cputcxy, _cputc
diff --git a/libsrc/atari/cputc.s b/libsrc/atari/cputc.s
index cf66fdacf..ec7564103 100644
--- a/libsrc/atari/cputc.s
+++ b/libsrc/atari/cputc.s
@@ -4,6 +4,8 @@
 ; void cputcxy (unsigned char x, unsigned char y, char c);
 ; void cputc (char c);
 ;
+; Important note: The implementation of cputs() relies on the cputc() function
+; not clobbering ptr1. Beware when rewriting or changing this function!
 
         .export         _cputcxy, _cputc
         .export         plot, cputdirect, putchar
diff --git a/libsrc/atari5200/cputc.s b/libsrc/atari5200/cputc.s
index 3e3a36cff..a39510237 100644
--- a/libsrc/atari5200/cputc.s
+++ b/libsrc/atari5200/cputc.s
@@ -5,6 +5,8 @@
 ; void cputcxy (unsigned char x, unsigned char y, char c);
 ; void cputc (char c);
 ;
+; Important note: The implementation of cputs() relies on the cputc() function
+; not clobbering ptr1. Beware when rewriting or changing this function!
 
         .include        "atari5200.inc"
 
diff --git a/libsrc/atari7800/cputc.s b/libsrc/atari7800/cputc.s
index 9ec84bfe5..56473255e 100644
--- a/libsrc/atari7800/cputc.s
+++ b/libsrc/atari7800/cputc.s
@@ -4,6 +4,8 @@
 ; void cputcxy (unsigned char x, unsigned char y, char c);
 ; void cputc (char c);
 ;
+; Important note: The implementation of cputs() relies on the cputc() function
+; not clobbering ptr1. Beware when rewriting or changing this function!
 
         .export         _cputc
         .import         gotox, gotoy, pusha0
diff --git a/libsrc/atmos/cputc.s b/libsrc/atmos/cputc.s
index db3fa373d..f649bb64d 100644
--- a/libsrc/atmos/cputc.s
+++ b/libsrc/atmos/cputc.s
@@ -5,6 +5,8 @@
 ; void cputcxy (unsigned char x, unsigned char y, char c);
 ; void cputc (char c);
 ;
+; Important note: The implementation of cputs() relies on the cputc() function
+; not clobbering ptr1. Beware when rewriting or changing this function!
 
         .export         _cputcxy, _cputc
         .export         setscrptr, cputdirect, putchar
diff --git a/libsrc/c128/cputc.s b/libsrc/c128/cputc.s
index 5c0760e75..9077c9472 100644
--- a/libsrc/c128/cputc.s
+++ b/libsrc/c128/cputc.s
@@ -5,6 +5,8 @@
 ; void cputcxy (unsigned char x, unsigned char y, char c);
 ; void cputc (char c);
 ;
+; Important note: The implementation of cputs() relies on the cputc() function
+; not clobbering ptr1. Beware when rewriting or changing this function!
 
         .export         _cputcxy, _cputc, cputdirect, putchar
         .export         newline, plot
diff --git a/libsrc/c64/cputc.s b/libsrc/c64/cputc.s
index b893f2102..759377f4a 100644
--- a/libsrc/c64/cputc.s
+++ b/libsrc/c64/cputc.s
@@ -4,6 +4,8 @@
 ; void __fastcall__ cputcxy (unsigned char x, unsigned char y, char c);
 ; void __fastcall__ cputc (char c);
 ;
+; Important note: The implementation of cputs() relies on the cputc() function
+; not clobbering ptr1. Beware when rewriting or changing this function!
 
         .export         _cputcxy, _cputc, cputdirect, putchar
         .export         newline, plot
diff --git a/libsrc/c65/cputc.s b/libsrc/c65/cputc.s
index 1a8dd1fee..926776df0 100644
--- a/libsrc/c65/cputc.s
+++ b/libsrc/c65/cputc.s
@@ -4,6 +4,8 @@
 ; void __fastcall__ cputcxy (unsigned char x, unsigned char y, char c);
 ; void __fastcall__ cputc (char c);
 ;
+; Important note: The implementation of cputs() relies on the cputc() function
+; not clobbering ptr1. Beware when rewriting or changing this function!
 
         .export         _cputcxy, _cputc, cputdirect, putchar
         .export         newline, plot
diff --git a/libsrc/cbm510/cputc.s b/libsrc/cbm510/cputc.s
index 7dd4cddb2..e26f2e233 100644
--- a/libsrc/cbm510/cputc.s
+++ b/libsrc/cbm510/cputc.s
@@ -4,6 +4,8 @@
 ; void cputcxy (unsigned char x, unsigned char y, char c);
 ; void cputc (char c);
 ;
+; Important note: The implementation of cputs() relies on the cputc() function
+; not clobbering ptr1. Beware when rewriting or changing this function!
 
         .export         _cputcxy, _cputc, cputdirect, putchar
         .export         newline, plot
diff --git a/libsrc/cbm610/cputc.s b/libsrc/cbm610/cputc.s
index 78e2a5581..6f016a4df 100644
--- a/libsrc/cbm610/cputc.s
+++ b/libsrc/cbm610/cputc.s
@@ -4,6 +4,8 @@
 ; void cputcxy (unsigned char x, unsigned char y, char c);
 ; void cputc (char c);
 ;
+; Important note: The implementation of cputs() relies on the cputc() function
+; not clobbering ptr1. Beware when rewriting or changing this function!
 
         .export         _cputcxy, _cputc, cputdirect, putchar
         .export         newline, plot
diff --git a/libsrc/conio/cputs.s b/libsrc/conio/cputs.s
index d6024c0e5..59fb8e050 100644
--- a/libsrc/conio/cputs.s
+++ b/libsrc/conio/cputs.s
@@ -22,6 +22,10 @@ _cputsxy:
 _cputs: sta     ptr1            ; Save s
         stx     ptr1+1
 
+; Important note: The implementation below relies on the _cputc() function not
+; clobbering ptr1. This might not be the case when rewriting this function so
+; beware!
+
 L0:
 .if .cap(CPU_HAS_ZPIND)
         lda     (ptr1)          ; (5)
diff --git a/libsrc/creativision/cputc.s b/libsrc/creativision/cputc.s
index 4389234c1..1ce3ec19f 100644
--- a/libsrc/creativision/cputc.s
+++ b/libsrc/creativision/cputc.s
@@ -5,6 +5,8 @@
 ; void cputcxy (unsigned char x, unsigned char y, char c);
 ; void cputc (char c);
 ;
+; Important note: The implementation of cputs() relies on the cputc() function
+; not clobbering ptr1. Beware when rewriting or changing this function!
 
         .export         _cputcxy, _cputc, cputdirect, putchar
         .export         newline
diff --git a/libsrc/cx16/cputc.s b/libsrc/cx16/cputc.s
index 22327d25a..6dc607312 100644
--- a/libsrc/cx16/cputc.s
+++ b/libsrc/cx16/cputc.s
@@ -4,6 +4,8 @@
 ; void __fastcall__ cputcxy (unsigned char x, unsigned char y, char c);
 ; void __fastcall__ cputc (char c);
 ;
+; Important note: The implementation of cputs() relies on the cputc() function
+; not clobbering ptr1. Beware when rewriting or changing this function!
 
         .export         _cputcxy, _cputc, cputdirect, putchar
         .export         newline, plot
diff --git a/libsrc/gamate/cputc.s b/libsrc/gamate/cputc.s
index a5d591d1e..f87471abd 100644
--- a/libsrc/gamate/cputc.s
+++ b/libsrc/gamate/cputc.s
@@ -2,6 +2,8 @@
 ; void cputcxy (unsigned char x, unsigned char y, char c);
 ; void cputc (char c);
 ;
+; Important note: The implementation of cputs() relies on the cputc() function
+; not clobbering ptr1. Beware when rewriting or changing this function!
 
         .export         _cputcxy, _cputc, cputdirect, putchar
         .export         newline, plot
diff --git a/libsrc/geos-common/conio/cputc.s b/libsrc/geos-common/conio/cputc.s
index af4194312..499d8fac0 100644
--- a/libsrc/geos-common/conio/cputc.s
+++ b/libsrc/geos-common/conio/cputc.s
@@ -21,6 +21,9 @@
 ; note that there are conflicts between control characters and keyboard:
 ; HOME = KEY_ENTER, KEY_HOME = REV_ON,
 ; UPLINE = ?, KEY_UPARROW = GOTOY, ...
+;
+; Important note: The implementation of cputs() relies on the cputc() function
+; not clobbering ptr1. Beware when rewriting or changing this function!
 
             .export _cputcxy, _cputc
             .import gotoxy, fixcursor
diff --git a/libsrc/mega65/cputc.s b/libsrc/mega65/cputc.s
index df44f5bdd..b6b376a7b 100644
--- a/libsrc/mega65/cputc.s
+++ b/libsrc/mega65/cputc.s
@@ -4,6 +4,8 @@
 ; void __fastcall__ cputcxy (unsigned char x, unsigned char y, char c);
 ; void __fastcall__ cputc (char c);
 ;
+; Important note: The implementation of cputs() relies on the cputc() function
+; not clobbering ptr1. Beware when rewriting or changing this function!
 
         .export         _cputcxy, _cputc, cputdirect, putchar
         .export         newline, plot
diff --git a/libsrc/nes/cputc.s b/libsrc/nes/cputc.s
index 209d22db2..3ecb47192 100644
--- a/libsrc/nes/cputc.s
+++ b/libsrc/nes/cputc.s
@@ -5,6 +5,8 @@
 ; void cputcxy (unsigned char x, unsigned char y, char c);
 ; void cputc (char c);
 ;
+; Important note: The implementation of cputs() relies on the cputc() function
+; not clobbering ptr1. Beware when rewriting or changing this function!
 
         .export         _cputcxy, _cputc, cputdirect, putchar
         .export         newline
diff --git a/libsrc/pce/cputc.s b/libsrc/pce/cputc.s
index 626d3ef8e..0dfbd1aca 100644
--- a/libsrc/pce/cputc.s
+++ b/libsrc/pce/cputc.s
@@ -2,6 +2,8 @@
 ; void cputcxy (unsigned char x, unsigned char y, char c);
 ; void cputc (char c);
 ;
+; Important note: The implementation of cputs() relies on the cputc() function
+; not clobbering ptr1. Beware when rewriting or changing this function!
 
         .export         _cputcxy, _cputc, cputdirect, putchar
         .export         newline, plot
diff --git a/libsrc/pet/cputc.s b/libsrc/pet/cputc.s
index 9b2c22323..2ee684ee8 100644
--- a/libsrc/pet/cputc.s
+++ b/libsrc/pet/cputc.s
@@ -4,6 +4,8 @@
 ; void cputcxy (unsigned char x, unsigned char y, char c);
 ; void cputc (char c);
 ;
+; Important note: The implementation of cputs() relies on the cputc() function
+; not clobbering ptr1. Beware when rewriting or changing this function!
 
         .export         _cputcxy, _cputc, cputdirect, putchar
         .export         newline, plot
diff --git a/libsrc/plus4/cputc.s b/libsrc/plus4/cputc.s
index a72b4012a..782d2e55c 100644
--- a/libsrc/plus4/cputc.s
+++ b/libsrc/plus4/cputc.s
@@ -4,6 +4,8 @@
 ; void cputcxy (unsigned char x, unsigned char y, char c);
 ; void cputc (char c);
 ;
+; Important note: The implementation of cputs() relies on the cputc() function
+; not clobbering ptr1. Beware when rewriting or changing this function!
 
         .export         _cputcxy, _cputc, cputdirect, putchar
         .export         newline, plot
diff --git a/libsrc/telestrat/cputc.s b/libsrc/telestrat/cputc.s
index 13714b32d..0abdc78ca 100644
--- a/libsrc/telestrat/cputc.s
+++ b/libsrc/telestrat/cputc.s
@@ -1,8 +1,10 @@
 ; 2018-04-13, Jede (jede@oric.org)
 ;
-
+;
 ; void cputc (char c);
 ;
+; Important note: The implementation of cputs() relies on the cputc() function
+; not clobbering ptr1. Beware when rewriting or changing this function!
 
         .export         _cputc, _cputcxy, cputdirect, display_conio
         .export         CHARCOLOR, OLD_CHARCOLOR, BGCOLOR, OLD_BGCOLOR
diff --git a/libsrc/vic20/cputc.s b/libsrc/vic20/cputc.s
index a6919ceaf..b0a3d2ef5 100644
--- a/libsrc/vic20/cputc.s
+++ b/libsrc/vic20/cputc.s
@@ -5,6 +5,8 @@
 ; void cputcxy (unsigned char x, unsigned char y, char c);
 ; void cputc (char c);
 ;
+; Important note: The implementation of cputs() relies on the cputc() function
+; not clobbering ptr1. Beware when rewriting or changing this function!
 
         .export         _cputcxy, _cputc, cputdirect, putchar
         .export         newline, plot