diff --git a/src/renderer/source_map.rs b/src/renderer/source_map.rs
index e2e4b61..44b773b 100644
--- a/src/renderer/source_map.rs
+++ b/src/renderer/source_map.rs
@@ -379,6 +379,19 @@ impl<'a> SourceMap<'a> {
             }
             line_count
         }
+
+        let source_len = self.source.len();
+        if let Some(bigger) = patches.iter().find_map(|x| {
+            // Allow patching one past the last character in the source.
+            if source_len + 1 < x.span.end {
+                Some(&x.span)
+            } else {
+                None
+            }
+        }) {
+            panic!("Patch span `{bigger:?}` is beyond the end of buffer `{source_len}`")
+        }
+
         // Assumption: all spans are in the same file, and all spans
         // are disjoint. Sort in ascending order.
         patches.sort_by_key(|p| p.span.start);
diff --git a/tests/formatter.rs b/tests/formatter.rs
index eca0b82..1d21d13 100644
--- a/tests/formatter.rs
+++ b/tests/formatter.rs
@@ -2635,3 +2635,121 @@ fn empty_span_start_line() {
     let renderer = Renderer::plain();
     assert_data_eq!(renderer.render(input), expected);
 }
+
+#[test]
+fn suggestion_span_one_bigger_than_source() {
+    let snippet_source = r#"#![allow(unused)]
+fn main() {
+[1, 2, 3].into_iter().for_each(|n| { *n; });
+}
+"#;
+
+    let suggestion_source = r#"[1, 2, 3].into_iter().for_each(|n| { *n; });
+"#;
+
+    let long_title1 ="this method call resolves to `<&[T; N] as IntoIterator>::into_iter` (due to backwards compatibility), but will resolve to `<[T; N] as IntoIterator>::into_iter` in Rust 2021";
+    let long_title2 = "for more information, see <https://doc.rust-lang.org/nightly/edition-guide/rust-2021/IntoIterator-for-arrays.html>";
+    let long_title3 = "or use `IntoIterator::into_iter(..)` instead of `.into_iter()` to explicitly iterate by value";
+
+    let input = &[
+        Group::with_title(Level::WARNING.title(long_title1))
+            .element(
+                Snippet::source(snippet_source)
+                    .path("lint_example.rs")
+                    .annotation(AnnotationKind::Primary.span(40..49)),
+            )
+            .element(Level::WARNING.message("this changes meaning in Rust 2021"))
+            .element(Level::NOTE.message(long_title2))
+            .element(Level::NOTE.message("`#[warn(array_into_iter)]` on by default")),
+        Group::with_title(
+            Level::HELP.title("use `.iter()` instead of `.into_iter()` to avoid ambiguity"),
+        )
+        .element(
+            Snippet::source(suggestion_source)
+                .path("lint_example.rs")
+                .line_start(3)
+                .patch(Patch::new(10..19, "iter")),
+        ),
+        Group::with_title(Level::HELP.title(long_title3)).element(
+            Snippet::source(suggestion_source)
+                .path("lint_example.rs")
+                .line_start(3)
+                .patch(Patch::new(
+                    suggestion_source.len() + 1..suggestion_source.len() + 1,
+                    "IntoIterator::into_iter(",
+                )),
+        ),
+    ];
+
+    let expected = str![[r#"
+warning: this method call resolves to `<&[T; N] as IntoIterator>::into_iter` (due to backwards compatibility), but will resolve to `<[T; N] as IntoIterator>::into_iter` in Rust 2021
+ --> lint_example.rs:3:11
+  |
+3 | [1, 2, 3].into_iter().for_each(|n| { *n; });
+  |           ^^^^^^^^^
+  |
+  = warning: this changes meaning in Rust 2021
+  = note: for more information, see <https://doc.rust-lang.org/nightly/edition-guide/rust-2021/IntoIterator-for-arrays.html>
+  = note: `#[warn(array_into_iter)]` on by default
+help: use `.iter()` instead of `.into_iter()` to avoid ambiguity
+  |
+3 - [1, 2, 3].into_iter().for_each(|n| { *n; });
+3 + [1, 2, 3].iter().for_each(|n| { *n; });
+  |
+help: or use `IntoIterator::into_iter(..)` instead of `.into_iter()` to explicitly iterate by value
+  |
+3 | IntoIterator::into_iter(
+  |
+"#]];
+    let renderer = Renderer::plain();
+    assert_data_eq!(renderer.render(input), expected);
+}
+
+#[test]
+#[should_panic = "Patch span `47..47` is beyond the end of buffer `45`"]
+fn suggestion_span_bigger_than_source() {
+    let snippet_source = r#"#![allow(unused)]
+fn main() {
+[1, 2, 3].into_iter().for_each(|n| { *n; });
+}
+"#;
+    let suggestion_source = r#"[1, 2, 3].into_iter().for_each(|n| { *n; });
+"#;
+
+    let long_title1 ="this method call resolves to `<&[T; N] as IntoIterator>::into_iter` (due to backwards compatibility), but will resolve to `<[T; N] as IntoIterator>::into_iter` in Rust 2021";
+    let long_title2 = "for more information, see <https://doc.rust-lang.org/nightly/edition-guide/rust-2021/IntoIterator-for-arrays.html>";
+    let long_title3 = "or use `IntoIterator::into_iter(..)` instead of `.into_iter()` to explicitly iterate by value";
+
+    let input = &[
+        Group::with_title(Level::WARNING.title(long_title1))
+            .element(
+                Snippet::source(snippet_source)
+                    .path("lint_example.rs")
+                    .annotation(AnnotationKind::Primary.span(40..49)),
+            )
+            .element(Level::WARNING.message("this changes meaning in Rust 2021"))
+            .element(Level::NOTE.message(long_title2))
+            .element(Level::NOTE.message("`#[warn(array_into_iter)]` on by default")),
+        Group::with_title(
+            Level::HELP.title("use `.iter()` instead of `.into_iter()` to avoid ambiguity"),
+        )
+        .element(
+            Snippet::source(suggestion_source)
+                .path("lint_example.rs")
+                .line_start(3)
+                .patch(Patch::new(10..19, "iter")),
+        ),
+        Group::with_title(Level::HELP.title(long_title3)).element(
+            Snippet::source(suggestion_source)
+                .path("lint_example.rs")
+                .line_start(3)
+                .patch(Patch::new(
+                    suggestion_source.len() + 2..suggestion_source.len() + 2,
+                    "IntoIterator::into_iter(",
+                )),
+        ),
+    ];
+
+    let renderer = Renderer::plain();
+    renderer.render(input);
+}