diff --git a/src/ca65/pseudo.c b/src/ca65/pseudo.c
index 5ce4e8c6e..88f609e25 100644
--- a/src/ca65/pseudo.c
+++ b/src/ca65/pseudo.c
@@ -642,7 +642,7 @@ static void DoCharMap (void)
 
     /* Read the index as numerical value */
     Index = ConstExpression ();
-    if (IsByteRange (Index)) {
+    if (!IsByteRange (Index)) {
         /* Value out of range */
         ErrorSkip ("Index must be in byte range");
         return;
diff --git a/test/asm/val/charmap.s b/test/asm/val/charmap.s
new file mode 100644
index 000000000..0a908ef13
--- /dev/null
+++ b/test/asm/val/charmap.s
@@ -0,0 +1,43 @@
+    .setcpu "6502"
+
+    .import _exit
+    .export _main
+
+    .charmap $41, 0
+    .charmap $42, 1
+    .charmap $43, 2
+mapped:
+    .byte "ABC"
+
+    .include "ascii_charmap.inc"
+ascii:
+    .byte "ABC"
+
+_main:
+    ldx #$01
+
+    lda mapped+0
+    cmp #0
+    bne error
+    lda mapped+1
+    cmp #1
+    bne error
+    lda mapped+2
+    cmp #2
+    bne error
+
+    lda ascii+0
+    cmp #$41
+    bne error
+    lda ascii+1
+    cmp #$42
+    bne error
+    lda ascii+2
+    cmp #$43
+    bne error
+
+    ldx #$00
+
+error:
+    txa
+    jmp _exit