diff --git a/src/cargo/util/toml/mod.rs b/src/cargo/util/toml/mod.rs
index 0ffeda2ada8..f4c3b9034c7 100644
--- a/src/cargo/util/toml/mod.rs
+++ b/src/cargo/util/toml/mod.rs
@@ -121,7 +121,7 @@ fn read_manifest_from_str(
                 .rfind('\n')
                 .map(|s| s + 1)
                 .unwrap_or(0);
-            let source_end = contents[span.end - 1..]
+            let source_end = contents[span.end.saturating_sub(1)..]
                 .find('\n')
                 .map(|s| s + span.end)
                 .unwrap_or(contents.len());
diff --git a/tests/testsuite/diagnostics.rs b/tests/testsuite/diagnostics.rs
new file mode 100644
index 00000000000..2de841825f2
--- /dev/null
+++ b/tests/testsuite/diagnostics.rs
@@ -0,0 +1,30 @@
+use cargo_test_support::project;
+
+#[cargo_test]
+fn dont_panic_on_render() {
+    let p = project()
+        .file(
+            "Cargo.toml",
+            r#"
+[package]
+name = "foo"
+version = "0.1.0"
+edition = "2021"
+[[bench.foo]]
+"#,
+        )
+        .file("src/lib.rs", "")
+        .build();
+
+    p.cargo("check")
+        .with_status(101)
+        .with_stderr(
+            "\
+error: invalid type: map, expected a sequence
+--> Cargo.toml:1:1
+ |
+ |
+",
+        )
+        .run();
+}
diff --git a/tests/testsuite/main.rs b/tests/testsuite/main.rs
index 4643f25f834..1ec140d7618 100644
--- a/tests/testsuite/main.rs
+++ b/tests/testsuite/main.rs
@@ -79,6 +79,7 @@ mod cross_publish;
 mod custom_target;
 mod death;
 mod dep_info;
+mod diagnostics;
 mod direct_minimal_versions;
 mod directory;
 mod doc;