diff --git a/tests/system.rs b/tests/system.rs
index 212e23f4f10..c1d838169ae 100644
--- a/tests/system.rs
+++ b/tests/system.rs
@@ -75,7 +75,7 @@ fn checkstyle_test() {
 // to a known output file generated by one of the write modes.
 fn assert_output(source: &Path, expected_filename: &Path) {
     let config = read_config(source);
-    let (file_map, _report) = format_file(source, &config);
+    let (_error_summary, file_map, _report) = format_file(source, &config);
 
     // Populate output by writing to a vec.
     let mut out = vec![];
@@ -214,8 +214,10 @@ where
                 fails += 1;
             }
             Ok(report) => reports.push(report),
-            Err(msg) => {
-                print_mismatches(msg);
+            Err(err) => {
+                if let IdempotentCheckError::Mismatch(msg) = err {
+                    print_mismatches(msg);
+                }
                 fails += 1;
             }
         }
@@ -263,20 +265,24 @@ fn read_config(filename: &Path) -> Config {
     config
 }
 
-fn format_file<P: Into<PathBuf>>(filepath: P, config: &Config) -> (FileMap, FormatReport) {
+fn format_file<P: Into<PathBuf>>(filepath: P, config: &Config) -> (Summary, FileMap, FormatReport) {
     let filepath = filepath.into();
     let input = Input::File(filepath);
-    let (_error_summary, file_map, report) =
-        format_input::<io::Stdout>(input, config, None).unwrap();
-    (file_map, report)
+    format_input::<io::Stdout>(input, config, None).unwrap()
 }
 
-pub fn idempotent_check(
-    filename: PathBuf,
-) -> Result<FormatReport, HashMap<PathBuf, Vec<Mismatch>>> {
+pub enum IdempotentCheckError {
+    Mismatch(HashMap<PathBuf, Vec<Mismatch>>),
+    Parse,
+}
+
+pub fn idempotent_check(filename: PathBuf) -> Result<FormatReport, IdempotentCheckError> {
     let sig_comments = read_significant_comments(&filename);
     let config = read_config(&filename);
-    let (file_map, format_report) = format_file(filename, &config);
+    let (error_summary, file_map, format_report) = format_file(filename, &config);
+    if error_summary.has_parsing_errors() {
+        return Err(IdempotentCheckError::Parse);
+    }
 
     let mut write_result = HashMap::new();
     for &(ref filename, ref text) in &file_map {
@@ -361,7 +367,7 @@ fn read_significant_comments(file_name: &Path) -> HashMap<String, String> {
 fn handle_result(
     result: HashMap<PathBuf, String>,
     target: Option<&str>,
-) -> Result<(), HashMap<PathBuf, Vec<Mismatch>>> {
+) -> Result<(), IdempotentCheckError> {
     let mut failures = HashMap::new();
 
     for (file_name, fmt_text) in result {
@@ -388,7 +394,7 @@ fn handle_result(
     if failures.is_empty() {
         Ok(())
     } else {
-        Err(failures)
+        Err(IdempotentCheckError::Mismatch(failures))
     }
 }