diff --git a/src/formatter/indent_remover.rs b/src/formatter/indent_remover.rs
index 132e78b..5699a47 100644
--- a/src/formatter/indent_remover.rs
+++ b/src/formatter/indent_remover.rs
@@ -6,11 +6,15 @@ impl Formatter for IndentRemover {
         let mut cursor = byte_pos;
         let bytes = content.as_bytes();
 
-        if !content.is_char_boundary(cursor) || bytes[cursor] != b'\n' {
+        if cursor >= bytes.len() || !content.is_char_boundary(cursor) || bytes[cursor] != b'\n' {
             return cursor;
         }
 
         let found = loop {
+            if cursor == 0 {
+                break false;
+            }
+
             cursor = cursor - 1;
 
             let current = bytes.get(cursor);
@@ -27,10 +31,6 @@ impl Formatter for IndentRemover {
                     _ => break false,
                 };
             }
-
-            if cursor == 0 {
-                break false;
-            }
         };
 
         if found {
@@ -105,5 +105,11 @@ mod tests {
         //                 |         ^
         let mut content = "+<div>+  あ  +    +    foo</div>".replace('+', "\n");
         assert_eq!(remover.format(&mut content, 10), 10);
+
+        let mut content = "".to_string();
+        assert_eq!(remover.format(&mut content, 0), 0);
+
+        let mut content = "\n".to_string();
+        assert_eq!(remover.format(&mut content, 0), 0);
     }
 }
diff --git a/src/formatter/prev_line_break_remover.rs b/src/formatter/prev_line_break_remover.rs
index b13436b..abff1b9 100644
--- a/src/formatter/prev_line_break_remover.rs
+++ b/src/formatter/prev_line_break_remover.rs
@@ -5,10 +5,17 @@ pub struct PrevLineBreakRemover {}
 impl Formatter for PrevLineBreakRemover {
     fn format(&self, content: &mut String, byte_pos: usize) -> usize {
         let mut cursor = byte_pos;
-
         let bytes = content.as_bytes();
 
+        if cursor >= bytes.len() {
+            return cursor;
+        }
+
         let line_break_pos = loop {
+            if cursor == 0 {
+                break None;
+            }
+
             cursor = cursor - 1;
 
             let current = bytes.get(cursor);
@@ -21,10 +28,6 @@ impl Formatter for PrevLineBreakRemover {
                     _ => break None,
                 };
             }
-
-            if cursor == 0 {
-                break None;
-            }
         };
 
         if let Some(line_break_pos) = line_break_pos {
@@ -115,5 +118,8 @@ mod tests {
             content,
             "aaa+ あ</div>".replace('+', "\n")
         );
+
+        let mut content = "\n".to_string();
+        assert_eq!(remover.format(&mut content, 0), 0);
     }
 }