diff --git a/src/as/error.c b/src/as/error.c
new file mode 100644
index 0000000..704658b
--- /dev/null
+++ b/src/as/error.c
@@ -0,0 +1,46 @@
+/* error.c
+ *
+ *   Copyright (C) 2018   Henrik Hautakoski <henrik.hautakoski@gmail.com>
+ *
+ *   This program is free software; you can redistribute it and/or modify
+ *   it under the terms of the GNU General Public License as published by
+ *   the Free Software Foundation; either version 2 of the License, or
+ *   (at your option) any later version.
+ *
+ *   This program is distributed in the hope that it will be useful,
+ *   but WITHOUT ANY WARRANTY; without even the implied warranty of
+ *   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ *   GNU General Public License for more details.
+ *
+ *   You should have received a copy of the GNU General Public License
+ *   along with this program; if not, write to the Free Software
+ *   Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston,
+ *   MA 02110-1301, USA.
+ */
+#include <stdio.h>
+#include <stdarg.h>
+#include "error.h"
+
+void asm_warn(int lineno, const char *fmt, ...) {
+
+	va_list vl;
+
+	fprintf(stderr, "Line %i: Warning: ", lineno);
+	va_start(vl, fmt);
+	vfprintf(stderr, fmt, vl);
+	va_end(vl);
+	fprintf(stderr, "\n");
+}
+
+int asm_error(int lineno, const char *fmt, ...) {
+
+	va_list vl;
+
+	fprintf(stderr, "Line %i: Error: ", lineno);
+	va_start(vl, fmt);
+	vfprintf(stderr, fmt, vl);
+	va_end(vl);
+	fprintf(stderr, "\n");
+
+	return -1;
+}
diff --git a/src/as/error.h b/src/as/error.h
new file mode 100644
index 0000000..70ebb71
--- /dev/null
+++ b/src/as/error.h
@@ -0,0 +1,27 @@
+/* error.h
+ *
+ *   Copyright (C) 2018   Henrik Hautakoski <henrik.hautakoski@gmail.com>
+ *
+ *   This program is free software; you can redistribute it and/or modify
+ *   it under the terms of the GNU General Public License as published by
+ *   the Free Software Foundation; either version 2 of the License, or
+ *   (at your option) any later version.
+ *
+ *   This program is distributed in the hope that it will be useful,
+ *   but WITHOUT ANY WARRANTY; without even the implied warranty of
+ *   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ *   GNU General Public License for more details.
+ *
+ *   You should have received a copy of the GNU General Public License
+ *   along with this program; if not, write to the Free Software
+ *   Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston,
+ *   MA 02110-1301, USA.
+ */
+#ifndef ASM_ERROR_H
+#define ASM_ERROR_H
+
+void asm_warn(int lineno, const char *fmt, ...);
+
+int asm_error(int lineno, const char *fmt, ...);
+
+#endif /* ASM_ERROR_H */