diff --git a/src/parser/ValidationError.ts b/src/parser/ValidationError.ts
new file mode 100644
index 0000000..c56501d
--- /dev/null
+++ b/src/parser/ValidationError.ts
@@ -0,0 +1,5 @@
+export class ValidationError extends Error {
+  constructor(msg: string) {
+    super(msg);
+  }
+}
diff --git a/src/parser/index.ts b/src/parser/index.ts
index 71f2bae..8ce650d 100644
--- a/src/parser/index.ts
+++ b/src/parser/index.ts
@@ -1,5 +1,6 @@
 import { Workout } from "../ast";
 import { parseTokens } from "./parser";
 import { tokenize } from "./tokenizer";
+import { validate } from "./validate";
 
-export const parse = (source: string): Workout => parseTokens(tokenize(source));
+export const parse = (source: string): Workout => validate(parseTokens(tokenize(source)));
diff --git a/src/parser/parser.test.ts b/src/parser/parser.test.ts
index 5a71658..28a437e 100644
--- a/src/parser/parser.test.ts
+++ b/src/parser/parser.test.ts
@@ -526,4 +526,17 @@ Rest: 5:00 50%
       }
     `);
   });
+
+  it("throws error when comment offset is outside of interval length", () => {
+    expect(() =>
+      parse(`
+Name: My Workout
+Interval: 2:00 90%
+  @ 0:00 Find your rythm.
+  @ 3:10 Try to settle in for the effort
+`),
+    ).toThrowErrorMatchingInlineSnapshot(
+      `"Comment \\"@ 190 Try to settle in for the effort\\" has offset outside of interval"`,
+    );
+  });
 });
diff --git a/src/parser/validate.ts b/src/parser/validate.ts
new file mode 100644
index 0000000..c5ce2d8
--- /dev/null
+++ b/src/parser/validate.ts
@@ -0,0 +1,19 @@
+import { Workout, Interval, Comment } from "../ast";
+import { ValidationError } from "./ValidationError";
+
+const isCommentWithinInterval = (comment: Comment, interval: Interval): boolean => {
+  return comment.offset.seconds < interval.duration.seconds;
+};
+
+const validateCommentOffsets = (interval: Interval) => {
+  for (const comment of interval.comments) {
+    if (!isCommentWithinInterval(comment, interval)) {
+      throw new ValidationError(`Comment "@ ${comment.offset.seconds} ${comment.text}" has offset outside of interval`);
+    }
+  }
+};
+
+export const validate = (workout: Workout): Workout => {
+  workout.intervals.forEach(validateCommentOffsets);
+  return workout;
+};