diff --git a/apps/zasm/main.asm b/apps/zasm/main.asm
index 177a789..8ee4477 100644
--- a/apps/zasm/main.asm
+++ b/apps/zasm/main.asm
@@ -15,6 +15,10 @@
 .equ	ZASM_ORG		ZASM_CTX_PC+2
 .equ	ZASM_RAMEND		ZASM_ORG+2
 
+; *** Errors ***
+; Unknown instruction or directive
+.equ	ERR_UNKWN		0x01
+
 ; Read file through blockdev ID in H and outputs its upcodes through blockdev
 ; ID in L.
 zasmMain:
@@ -98,7 +102,7 @@ zasmParseFile:
 ; resulting opcode(s) through ioPutC and increases (IO_PC) by the number of
 ; bytes written. BC is set to the result of the call to tokenize.
 ; Sets Z if parse was successful, unset if there was an error. EOF is not an
-; error.
+; error. If there is an error, A is set to the corresponding error code (ERR_*).
 parseLine:
 	call	tokenize
 	ld	a, b		; TOK_*
@@ -109,9 +113,10 @@ parseLine:
 	cp	TOK_LABEL
 	jr	z, _parseLabel
 	cp	TOK_EOF
-	ret			; Z is correct. If EOF, Z is set and not an
-				; error, otherwise, it means bad token and
-				; errors out.
+	ret	z		; We're finished, no error.
+	; Bad token
+	ld	a, ERR_UNKWN
+	jp	unsetZ		; return with Z unset
 
 _parseInstr:
 	ld	a, c		; I_*
diff --git a/tools/emul/zasm/zasm.bin b/tools/emul/zasm/zasm.bin
index 162e76e..8194765 100644
Binary files a/tools/emul/zasm/zasm.bin and b/tools/emul/zasm/zasm.bin differ
diff --git a/tools/emul/zasm/zasm.c b/tools/emul/zasm/zasm.c
index 19fe986..f3bc0fb 100644
--- a/tools/emul/zasm/zasm.c
+++ b/tools/emul/zasm/zasm.c
@@ -188,9 +188,10 @@ int main()
     }
 #endif
     fflush(stdout);
-#ifdef DEBUG
-    fprintf(stderr, "Ended with A=%d DE=%d\n", cpu.R1.br.A, cpu.R1.wr.DE);
-#endif
-    return 0;
+    int res = cpu.R1.br.A;
+    if (res != 0) {
+        fprintf(stderr, "Error %d\n", res);
+    }
+    return res;
 }
 
diff --git a/tools/tests/zasm/errtests.sh b/tools/tests/zasm/errtests.sh
new file mode 100755
index 0000000..a9e9de9
--- /dev/null
+++ b/tools/tests/zasm/errtests.sh
@@ -0,0 +1,20 @@
+#!/bin/sh
+
+# no "set -e" because we test errors
+
+ZASM=../../emul/zasm/zasm
+
+chkerr() {
+    echo "Check that '$1' results in error $2"
+    ${ZASM} <<< $1 > /dev/null
+    local res=$?
+    if [[ $res == $2 ]]; then
+        echo "Good!"
+    else
+        echo "$res != $2"
+        exit 1
+    fi
+}
+
+chkerr "foo" 1
+
diff --git a/tools/tests/zasm/runtests.sh b/tools/tests/zasm/runtests.sh
index d7b82db..a97c8e2 100755
--- a/tools/tests/zasm/runtests.sh
+++ b/tools/tests/zasm/runtests.sh
@@ -23,7 +23,7 @@ cmpas() {
     fi
 }
 
-for fn in *.asm; do
+for fn in test*.asm; do
     echo "Comparing ${fn}"
     cmpas $fn
 done
@@ -34,3 +34,4 @@ while read line; do
     cmpas ${TMPFILE}
 done
 
+./errtests.sh