diff --git a/src/config/file_lines.rs b/src/config/file_lines.rs
index 436c7a83b81..58f65b3c1b6 100644
--- a/src/config/file_lines.rs
+++ b/src/config/file_lines.rs
@@ -16,6 +16,7 @@ use std::rc::Rc;
 use std::{cmp, fmt, iter, str};
 
 use serde::de::{Deserialize, Deserializer};
+use serde::ser::{self, Serialize, Serializer};
 use serde_json as json;
 
 use syntax::codemap::{self, FileMap};
@@ -53,6 +54,36 @@ impl fmt::Display for FileName {
     }
 }
 
+impl<'de> Deserialize<'de> for FileName {
+    fn deserialize<D>(deserializer: D) -> Result<FileName, D::Error>
+    where
+        D: Deserializer<'de>,
+    {
+        let s = String::deserialize(deserializer)?;
+        if s == "stdin" {
+            Ok(FileName::Stdin)
+        } else {
+            Ok(FileName::Real(s.into()))
+        }
+    }
+}
+
+impl Serialize for FileName {
+    fn serialize<S>(&self, serializer: S) -> Result<S::Ok, S::Error>
+    where
+        S: Serializer,
+    {
+        let s = match self {
+            FileName::Stdin => Ok("stdin"),
+            FileName::Real(path) => path
+                .to_str()
+                .ok_or_else(|| ser::Error::custom("path can't be serialized as UTF-8 string")),
+        };
+
+        s.and_then(|s| serializer.serialize_str(s))
+    }
+}
+
 impl LineRange {
     pub fn file_name(&self) -> FileName {
         self.file.name.clone().into()
@@ -175,6 +206,20 @@ impl FileLines {
         Files(self.0.as_ref().map(|m| m.keys()))
     }
 
+    /// Returns JSON representation as accepted by the `--file-lines JSON` arg.
+    pub fn to_json_spans(&self) -> Vec<JsonSpan> {
+        match &self.0 {
+            None => vec![],
+            Some(file_ranges) => file_ranges
+                .iter()
+                .flat_map(|(file, ranges)| ranges.iter().map(move |r| (file, r)))
+                .map(|(file, range)| JsonSpan {
+                    file: file.to_owned(),
+                    range: (range.lo, range.hi),
+                }).collect(),
+        }
+    }
+
     /// Returns true if `self` includes all lines in all files. Otherwise runs `f` on all ranges in
     /// the designated file (if any) and returns true if `f` ever does.
     fn file_range_matches<F>(&self, file_name: &FileName, f: F) -> bool
@@ -249,22 +294,12 @@ impl str::FromStr for FileLines {
 }
 
 // For JSON decoding.
-#[derive(Clone, Debug, Deserialize)]
-struct JsonSpan {
-    #[serde(deserialize_with = "deserialize_filename")]
+#[derive(Clone, PartialEq, Eq, PartialOrd, Ord, Debug, Deserialize, Serialize)]
+pub struct JsonSpan {
     file: FileName,
     range: (usize, usize),
 }
 
-fn deserialize_filename<'de, D: Deserializer<'de>>(d: D) -> Result<FileName, D::Error> {
-    let s = String::deserialize(d)?;
-    if s == "stdin" {
-        Ok(FileName::Stdin)
-    } else {
-        Ok(FileName::Real(s.into()))
-    }
-}
-
 impl JsonSpan {
     fn into_tuple(self) -> Result<(FileName, Range), String> {
         let (lo, hi) = self.range;
@@ -350,4 +385,38 @@ mod test {
             Range::new(3, 7).merge(Range::new(4, 5))
         );
     }
+
+    use super::json::{self, json, json_internal};
+    use super::{FileLines, FileName};
+    use std::{collections::HashMap, path::PathBuf};
+
+    #[test]
+    fn file_lines_to_json() {
+        let ranges: HashMap<FileName, Vec<Range>> = [
+            (
+                FileName::Real(PathBuf::from("src/main.rs")),
+                vec![Range::new(1, 3), Range::new(5, 7)],
+            ),
+            (
+                FileName::Real(PathBuf::from("src/lib.rs")),
+                vec![Range::new(1, 7)],
+            ),
+        ]
+            .iter()
+            .cloned()
+            .collect();
+
+        let file_lines = FileLines::from_ranges(ranges);
+        let mut spans = file_lines.to_json_spans();
+        spans.sort();
+        let json = json::to_value(&spans).unwrap();
+        assert_eq!(
+            json,
+            json! {[
+                {"file": "src/lib.rs",  "range": [1, 7]},
+                {"file": "src/main.rs", "range": [1, 3]},
+                {"file": "src/main.rs", "range": [5, 7]},
+            ]}
+        );
+    }
 }