diff --git a/compiler/ast/ast.ts b/compiler/ast/ast.ts
index 4040f6e..2a16763 100644
--- a/compiler/ast/ast.ts
+++ b/compiler/ast/ast.ts
@@ -1,3 +1,5 @@
+import { Span } from "../diagnostics.ts";
+
 export type File = {
     stmts: Stmt[];
 };
@@ -5,6 +7,7 @@ export type File = {
 export type Stmt = {
     id: number;
     kind: StmtKind;
+    span: Span;
 };
 
 export type StmtKind =
diff --git a/compiler/main.ts b/compiler/main.ts
index fb99755..5dcf461 100644
--- a/compiler/main.ts
+++ b/compiler/main.ts
@@ -52,7 +52,7 @@ export class FileTreeCollector implements ast.Visitor<[_P]> {
     }
 
     visitModFileStmt(
-        _stmt: ast.Stmt,
+        stmt: ast.Stmt,
         kind: ast.ModFileStmt,
         { file }: _P,
     ): ast.VisitRes {
@@ -65,6 +65,7 @@ export class FileTreeCollector implements ast.Visitor<[_P]> {
                         severity: "fatal",
                         msg: `module '${ident}' already declared`,
                         file,
+                        span: stmt.span,
                     });
                 }
                 return new FileTreeCollector(
diff --git a/compiler/test_diagnostics.ts b/compiler/test_diagnostics.ts
new file mode 100644
index 0000000..8b0bfd9
--- /dev/null
+++ b/compiler/test_diagnostics.ts
@@ -0,0 +1,27 @@
+import { Ctx } from "./ctx.ts";
+import { prettyPrintReport } from "./diagnostics.ts";
+
+const ctx = new Ctx();
+
+const text = `
+make an error here
+`;
+
+const file = ctx.addFile(
+    "root",
+    "path/file.ts",
+    "path/file.ts",
+    undefined,
+    text,
+);
+
+prettyPrintReport(ctx, {
+    file,
+    msg: "an error",
+    severity: "error",
+    origin: "compiler",
+    span: {
+        begin: { idx: 6, line: 2, col: 6 },
+        end: { idx: 13, line: 2, col: 13 },
+    },
+});