diff --git a/assembler.js b/assembler.js
index 4901daf..7918794 100644
--- a/assembler.js
+++ b/assembler.js
@@ -78,7 +78,7 @@ function preparseSourceCode(source) {
   return lines.map((line, index) => {
     dbg(1, `  ${line}`);
     let info = {
-      number: index,
+      number: index + 1,
       source: line,
       sanitized: stripWhitespaceFromEnds(stripComments(line)),
       type: getLineType(line),