diff --git a/doc/ca65.sgml b/doc/ca65.sgml
index af762b90a..22704a30d 100644
--- a/doc/ca65.sgml
+++ b/doc/ca65.sgml
@@ -2130,10 +2130,10 @@ Here's a list of all control commands and a description, what they do:
 <sect1><tt>.CHARMAP</tt><label id=".CHARMAP"><p>
 
   Apply a custom mapping for characters. The command is followed by two
-  numbers in the range 1..255. The first one is the index of the source
-  character, the second one is the mapping. The mapping applies to all
-  character and string constants when they generate output, and overrides
-  a mapping table specified with the <tt><ref id="option-t" name="-t"></tt>
+  numbers. The first one is the index of the source character (range 1..255),
+  the second one is the mapping (range 0..255). The mapping applies to all
+  character and string constants when they generate output, and overrides a
+  mapping table specified with the <tt><ref id="option-t" name="-t"></tt>
   command line switch.
 
   Example:
diff --git a/src/ca65/pseudo.c b/src/ca65/pseudo.c
index 4bafb8626..58e2621b2 100644
--- a/src/ca65/pseudo.c
+++ b/src/ca65/pseudo.c
@@ -637,7 +637,7 @@ static void DoCharMap (void)
 
     /* Read the character code */
     Code = ConstExpression ();
-    if (Code <= 0 || Code > 255) {
+    if (Code < 0 || Code > 255) {
     	/* Value out of range */
        	ErrorSkip ("Range error");
     	return;