diff --git a/crates/ty_test/src/assertion.rs b/crates/ty_test/src/assertion.rs
index c62123b5fc..6f1e80f9c9 100644
--- a/crates/ty_test/src/assertion.rs
+++ b/crates/ty_test/src/assertion.rs
@@ -418,10 +418,14 @@ impl<'a> ErrorAssertionParser<'a> {
 
                 // message text
                 '"' => {
-                    let comment_source = self.comment_source.trim();
+                    let comment_source = self.comment_source.trim_end();
                     return if comment_source.ends_with('"') {
-                        let rest = &comment_source
-                            [self.cursor.offset().to_usize()..comment_source.len() - 1];
+                        let start = self.cursor.offset().to_usize();
+                        let end = comment_source.len() - 1;
+                        if start > end {
+                            return Err(ErrorAssertionParseError::DanglingMessageQuote);
+                        }
+                        let rest = &comment_source[start..end];
                         Ok(ErrorAssertion {
                             rule,
                             column,
@@ -489,6 +493,8 @@ pub(crate) enum ErrorAssertionParseError<'a> {
     MultipleRuleCodes,
     #[error("expected '\"' to be the final character in an assertion with an error message")]
     UnclosedMessage,
+    #[error("expected message text and closing '\"' after opening '\"'")]
+    DanglingMessageQuote,
     #[error(
         "unexpected character `{character}` at offset {offset} (relative to the `:` in the assertion comment)"
     )]
diff --git a/crates/ty_test/src/matcher.rs b/crates/ty_test/src/matcher.rs
index 06694fce55..ade91912f5 100644
--- a/crates/ty_test/src/matcher.rs
+++ b/crates/ty_test/src/matcher.rs
@@ -1395,4 +1395,28 @@ mod tests {
             )],
         );
     }
+
+    #[test]
+    fn trailing_quote_without_message_not_allowed() {
+        let source = "x  # error: [some-rule]\"";
+        let result = get_result(
+            source,
+            vec![ExpectedDiagnostic::new(
+                DiagnosticId::lint("some-rule"),
+                "some message",
+                0,
+            )],
+        );
+
+        assert_fail(
+            result,
+            &[(
+                0,
+                &[
+                    "invalid assertion: expected message text and closing '\"' after opening '\"'",
+                    r#"unexpected error: 1 [some-rule] "some message""#,
+                ],
+            )],
+        );
+    }
 }