diff --git a/CHANGELOG.md b/CHANGELOG.md
index 56b09a43..ed106ad5 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -20,9 +20,10 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
  - Moved tests to a separate disk (tests.d64).
  - gfx: Renamed ERASE to PEN.
  - #> (the pictured numeric output string buffer) now uses its own buffer chopped from the end of PAD.
- - CHAR, HEADER and other parsing words no longer do REFILL on missing text.
+ - CHAR no longer does REFILL on missing text.
  - EVALUATE now accepts multi-line strings.
  - ( refills to accept multi-line comments when parsing EVALUATE strings.
+ - Defining words based on HEADER now abort with an error on missing text.
 ### Removed
  - GETC, 100/, INTERPRET, ;CODE (replace with: RTS, END-CODE)
 ### Fixed
diff --git a/asm/compiler.asm b/asm/compiler.asm
index 4eba8d3e..61c8f866 100644
--- a/asm/compiler.asm
+++ b/asm/compiler.asm
@@ -135,19 +135,26 @@ COLON
 
     jmp RBRAC ; enter compile mode
 
-
-; --- HEADER ( name -- )
     +BACKLINK "header", 6
-HEADER
+HEADER ; ( "name" -- )
     inc last_word_no_tail_call_elimination
 
-    ; update dictionary
-
+    ; Parse, get [W2]name-addr and [LSB-2]length.
     jsr PARSE_NAME
-
-    ; update dictionary pointer
+    inx
     lda LSB, x
-    sta .putlen+1
+    sta W2
+    lda MSB, x
+    sta W2 + 1
+    inx
+
+    ; Abort if empty string.
+    lda LSB - 2, x
+    bne +
+    jmp .on_stack_underflow ; "err"
++   sta .putlen+1
+
+    ; Move back [W]LATEST.
     clc
     adc #3
     sta W
@@ -160,16 +167,13 @@ HEADER
     dec LATEST_MSB
 +   lda LATEST_MSB
     sta W + 1
+
+    ; Store name length.
     ldy #0
-    ; Store length byte.
-    lda LSB, x
+    lda LSB - 2, x
     sta (W), y
-    inx
-    lda LSB, x
-    sta W2
-    lda MSB, x
-    sta W2 + 1
-    ; copy string
+
+    ; Copy name.
 -   lda (W2), y
     jsr CHAR_TO_LOWERCASE
     iny
@@ -177,14 +181,14 @@ HEADER
 .putlen
     cpy #0
     bne -
-    ; store here
+
+    ; Store xt.
     iny
     lda HERE_LSB
     sta (W), y
     iny
     lda HERE_MSB
     sta (W), y
-    inx
     rts
 
     +BACKLINK "lit", 3
@@ -248,7 +252,7 @@ COMPILE_COMMA
     +BACKLINK "literal", 7 | F_IMMEDIATE
 LITERAL
     dex
-    lda MSB+1,x
+    lda MSB + 1,x
     bne +
     lda #<LITC
     sta LSB,x