diff --git a/src/lib.rs b/src/lib.rs
index 94b0cc2..6f013dd 100644
--- a/src/lib.rs
+++ b/src/lib.rs
@@ -8,42 +8,39 @@ use {
     syn::{parse, LitStr},
 };
 
+mod source_reader;
+
 struct ShaderModule {
-    source_file: std::path::PathBuf,
     source_text: String,
     naga_module: naga::Module,
 }
 
 impl ShaderModule {
     fn try_new(source_file: impl Into<std::path::PathBuf>) -> Result<Self, Error> {
-        let source_file = source_file.into();
-        let source_text = fs::read_to_string(&source_file).map_err(|err| {
-            Error::from_message(format!(
-                "Could not open \"{}\": {}",
-                &source_file.as_os_str().to_string_lossy(),
-                err
-            ))
-        })?;
+        let source_filename = source_file.into();
+        let source_file = source_reader::read_source_file(source_filename)?;
+        let source_text = source_file.full_text().to_string();
 
         let naga_module = wgsl::parse_str(&source_text).map_err(|err| {
             if let Some(location) = err.location(&source_text) {
+                let (inner_source_filename, inner_line_num) =
+                    source_file.map_source_line_num(location.line_number as usize);
                 Error::Message(format!(
                     "Error in {} at line {}, column {}:\n{}",
-                    &source_file.as_os_str().to_string_lossy(),
-                    location.line_number,
+                    &inner_source_filename.as_os_str().to_string_lossy(),
+                    inner_line_num,
                     location.line_position,
                     err.message()
                 ))
             } else {
                 Error::Message(format!(
                     "Error in {}:\n{}",
-                    &source_file.as_os_str().to_string_lossy(),
+                    &source_file.root_filename().as_os_str().to_string_lossy(),
                     err.message()
                 ))
             }
         })?;
         Ok(Self {
-            source_file,
             source_text,
             naga_module,
         })
diff --git a/src/source_reader.rs b/src/source_reader.rs
new file mode 100644
index 0000000..e6deccf
--- /dev/null
+++ b/src/source_reader.rs
@@ -0,0 +1,51 @@
+use {
+    crate::Error,
+    std::{
+        fs,
+        path::{Path, PathBuf},
+    },
+};
+
+struct SourceMap {
+    filename: PathBuf,
+    offset: usize,
+    total_lines: usize,
+    insertions: Vec<SourceMap>,
+}
+
+pub struct SourceFile {
+    source_text: String,
+    source_map: SourceMap,
+}
+
+impl SourceFile {
+    pub fn root_filename(&self) -> &Path {
+        &self.source_map.filename
+    }
+    pub fn full_text(&self) -> &str {
+        &self.source_text
+    }
+
+    pub fn map_source_line_num(&self, line_num: usize) -> (&Path, usize) {
+        (&self.source_map.filename, line_num)
+    }
+}
+
+pub fn read_source_file(filename: PathBuf) -> Result<SourceFile, Error> {
+    let source_text = fs::read_to_string(&filename).map_err(|err| {
+        Error::from_message(format!(
+            "Could not open \"{}\": {}",
+            &filename.as_os_str().to_string_lossy(),
+            err
+        ))
+    })?;
+    Ok(SourceFile {
+        source_text,
+        source_map: SourceMap {
+            filename,
+            offset: 0,
+            total_lines: 0,
+            insertions: vec![],
+        },
+    })
+}