diff --git a/src/string.rs b/src/string.rs
index b74e26224cd..b65aa5b33b2 100644
--- a/src/string.rs
+++ b/src/string.rs
@@ -278,11 +278,14 @@ fn break_string(max_width: usize, trim_end: bool, line_end: &str, input: &[&str]
         }
         cur_index
     };
+    if max_width_index_in_input == 0 {
+        return SnippetState::EndOfInput(input.concat());
+    }
 
     // Find the position in input for breaking the string
     if line_end.is_empty()
         && trim_end
-        && !is_whitespace(input[max_width_index_in_input.checked_sub(1).unwrap_or(0)])
+        && !is_whitespace(input[max_width_index_in_input - 1])
         && is_whitespace(input[max_width_index_in_input])
     {
         // At a breaking point already
@@ -301,7 +304,7 @@ fn break_string(max_width: usize, trim_end: bool, line_end: &str, input: &[&str]
         return if trim_end {
             SnippetState::LineEnd(input[..=url_index_end].concat(), index_plus_ws + 1)
         } else {
-            return SnippetState::LineEnd(input[..=index_plus_ws].concat(), index_plus_ws + 1);
+            SnippetState::LineEnd(input[..=index_plus_ws].concat(), index_plus_ws + 1)
         };
     }
 
diff --git a/tests/source/issue-5023.rs b/tests/source/issue-5023.rs
new file mode 100644
index 00000000000..ae1c723eff7
--- /dev/null
+++ b/tests/source/issue-5023.rs
@@ -0,0 +1,22 @@
+// rustfmt-wrap_comments: true
+
+/// A comment to test special unicode characters on boundaries
+/// 是，是，是，是，是，是，是，是，是，是，是，是  it should break right here this goes to the next line
+fn main() {
+    if xxx {
+        let xxx = xxx
+            .into_iter()
+            .filter(|(xxx, xxx)| {
+                if let Some(x) = Some(1) {
+                    // xxxxxxxxxxxxxxxxxx, xxxxxxxxxxxx, xxxxxxxxxxxxxxxxxxxx xxx xxxxxxx, xxxxx xxx
+                    // xxxxxxxxxx. xxxxxxxxxxxxxxxx，xxxxxxxxxxxxxxxxx xxx xxxxxxx
+                    // 是sdfadsdfxxxxxxxxx，sdfaxxxxxx_xxxxx_masdfaonxxx，
+                    if false {
+                        return true;
+                    }
+                }
+                false
+            })
+            .collect();
+    }
+}
diff --git a/tests/target/issue-5023.rs b/tests/target/issue-5023.rs
index d5b3722273d..4e84c7d9842 100644
--- a/tests/target/issue-5023.rs
+++ b/tests/target/issue-5023.rs
@@ -1,4 +1,8 @@
 // rustfmt-wrap_comments: true
+
+/// A comment to test special unicode characters on boundaries
+/// 是，是，是，是，是，是，是，是，是，是，是，是  it should break right here
+/// this goes to the next line
 fn main() {
     if xxx {
         let xxx = xxx