diff --git a/src/compare/util.rs b/src/compare/util.rs
index d12ee6d..1804cd9 100644
--- a/src/compare/util.rs
+++ b/src/compare/util.rs
@@ -1,5 +1,5 @@
 use super::sexp::Token;
-use crate::types::Source;
+use crate::types::StandardProperties;
 
 /// Check if the child string slice is a slice of the parent string slice.
 fn is_slice_of(parent: &str, child: &str) -> bool {
@@ -10,13 +10,16 @@ fn is_slice_of(parent: &str, child: &str) -> bool {
     child_start >= parent_start && child_end <= parent_end
 }
 
-/// Get the offset into source that the rust object exists at.
+/// Get the byte offset into source that the rust object exists at.
 ///
 /// These offsets are zero-based unlike the elisp ones.
-fn get_offsets<'s, S: Source<'s>>(source: &'s str, rust_object: &'s S) -> (usize, usize) {
-    let rust_object_source = rust_object.get_source();
-    assert!(is_slice_of(source, rust_object_source));
-    let offset = rust_object_source.as_ptr() as usize - source.as_ptr() as usize;
+fn get_rust_byte_offsets<'s, S: StandardProperties<'s>>(
+    original_document: &'s str,
+    rust_ast_node: &'s S,
+) -> (usize, usize) {
+    let rust_object_source = rust_ast_node.get_source();
+    debug_assert!(is_slice_of(original_document, rust_object_source));
+    let offset = rust_object_source.as_ptr() as usize - original_document.as_ptr() as usize;
     let end = offset + rust_object_source.len();
     (offset, end)
 }
@@ -40,24 +43,27 @@ pub(crate) fn assert_name<'s>(
     Ok(())
 }
 
-pub(crate) fn assert_bounds<'s, S: Source<'s>>(
-    source: &'s str,
+/// Assert that the character ranges defined by upstream org-mode's :standard-properties match the slices in Organic's StandardProperties.
+///
+/// This does **not** handle plain text because plain text is a special case.
+pub(crate) fn assert_bounds<'s, S: StandardProperties<'s>>(
+    original_document: &'s str,
     emacs: &'s Token<'s>,
     rust: &'s S,
 ) -> Result<(), Box<dyn std::error::Error>> {
-    let standard_properties = get_emacs_standard_properties(emacs)?;
+    let standard_properties = get_emacs_standard_properties(emacs)?; // 1-based
     let (begin, end) = (
         standard_properties
             .begin
             .ok_or("Token should have a begin.")?,
         standard_properties.end.ok_or("Token should have an end.")?,
     );
-    let (rust_begin, rust_end) = get_offsets(source, rust);
-    let rust_begin_char_offset = (&source[..rust_begin]).chars().count();
+    let (rust_begin, rust_end) = get_rust_byte_offsets(original_document, rust); // 0-based
+    let rust_begin_char_offset = (&original_document[..rust_begin]).chars().count() + 1; // 1-based
     let rust_end_char_offset =
-        rust_begin_char_offset + (&source[rust_begin..rust_end]).chars().count();
-    if (rust_begin_char_offset + 1) != begin || (rust_end_char_offset + 1) != end {
-        Err(format!("Rust bounds (in chars) ({rust_begin}, {rust_end}) do not match emacs bounds ({emacs_begin}, {emacs_end})", rust_begin = rust_begin_char_offset + 1, rust_end = rust_end_char_offset + 1, emacs_begin=begin, emacs_end=end))?;
+        rust_begin_char_offset + (&original_document[rust_begin..rust_end]).chars().count(); // 1-based
+    if rust_begin_char_offset != begin || rust_end_char_offset != end {
+        Err(format!("Rust bounds (in chars) ({rust_begin}, {rust_end}) do not match emacs bounds ({emacs_begin}, {emacs_end})", rust_begin = rust_begin_char_offset, rust_end = rust_end_char_offset, emacs_begin=begin, emacs_end=end))?;
     }
 
     Ok(())