diff --git a/src/rustfmt_diff.rs b/src/rustfmt_diff.rs
index 3fb22865385..c0aca68fe2f 100644
--- a/src/rustfmt_diff.rs
+++ b/src/rustfmt_diff.rs
@@ -47,7 +47,7 @@ pub fn make_diff(expected: &str, actual: &str, context_size: usize) -> Vec<Misma
     for result in diff::lines(expected, actual) {
         match result {
             diff::Result::Left(str) => {
-                if lines_since_mismatch >= context_size {
+                if lines_since_mismatch >= context_size && lines_since_mismatch > 0 {
                     results.push(mismatch);
                     mismatch = Mismatch::new(line_number - context_queue.len() as u32);
                 }
@@ -60,7 +60,7 @@ pub fn make_diff(expected: &str, actual: &str, context_size: usize) -> Vec<Misma
                 lines_since_mismatch = 0;
             }
             diff::Result::Right(str) => {
-                if lines_since_mismatch >= context_size {
+                if lines_since_mismatch >= context_size && lines_since_mismatch > 0 {
                     results.push(mismatch);
                     mismatch = Mismatch::new(line_number - context_queue.len() as u32);
                 }
@@ -80,7 +80,7 @@ pub fn make_diff(expected: &str, actual: &str, context_size: usize) -> Vec<Misma
 
                 if lines_since_mismatch < context_size {
                     mismatch.lines.push(DiffLine::Context(str.to_owned()));
-                } else {
+                } else if context_size > 0 {
                     context_queue.push_back(str);
                 }
 
@@ -162,3 +162,75 @@ where
         }
     }
 }
+
+#[cfg(test)]
+mod test {
+    use super::{make_diff, Mismatch};
+    use super::DiffLine::*;
+
+    #[test]
+    fn diff_simple() {
+        let src = "one\ntwo\nthree\nfour\nfive\n";
+        let dest = "one\ntwo\ntrois\nfour\nfive\n";
+        let diff = make_diff(src, dest, 1);
+        assert_eq!(
+            diff,
+            vec![
+                Mismatch {
+                    line_number: 2,
+                    lines: vec![
+                        Context("two".into()),
+                        Resulting("three".into()),
+                        Expected("trois".into()),
+                        Context("four".into()),
+                    ],
+                },
+            ]
+        );
+    }
+
+    #[test]
+    fn diff_simple2() {
+        let src = "one\ntwo\nthree\nfour\nfive\nsix\nseven\n";
+        let dest = "one\ntwo\ntrois\nfour\ncinq\nsix\nseven\n";
+        let diff = make_diff(src, dest, 1);
+        assert_eq!(
+            diff,
+            vec![
+                Mismatch {
+                    line_number: 2,
+                    lines: vec![
+                        Context("two".into()),
+                        Resulting("three".into()),
+                        Expected("trois".into()),
+                        Context("four".into()),
+                    ],
+                },
+                Mismatch {
+                    line_number: 5,
+                    lines: vec![
+                        Resulting("five".into()),
+                        Expected("cinq".into()),
+                        Context("six".into()),
+                    ],
+                },
+            ]
+        );
+    }
+
+    #[test]
+    fn diff_zerocontext() {
+        let src = "one\ntwo\nthree\nfour\nfive\n";
+        let dest = "one\ntwo\ntrois\nfour\nfive\n";
+        let diff = make_diff(src, dest, 0);
+        assert_eq!(
+            diff,
+            vec![
+                Mismatch {
+                    line_number: 3,
+                    lines: vec![Resulting("three".into()), Expected("trois".into())],
+                },
+            ]
+        );
+    }
+}