diff --git a/apps/gridcraft-cli/src/check.rs b/apps/gridcraft-cli/src/check.rs
index 2b8529876..c34a24fe8 100644
--- a/apps/gridcraft-cli/src/check.rs
+++ b/apps/gridcraft-cli/src/check.rs
@@ -141,7 +141,8 @@ pub struct FileReport {
     pub path: String,
     /// GridCraft couldn't open the file: its message.
     pub error: Option<String>,
-    pub warnings: usize,
+    /// Import warnings, in the order the importer produced them.
+    pub warnings: Vec<String>,
     pub calc: CalcReport,
     pub round_trip: RoundTrip,
 }
@@ -287,7 +288,7 @@ fn check_inner(path: &str, bytes: &[u8], opts: &Options) -> FileReport {
             return report;
         }
     };
-    report.warnings = warnings.len();
+    report.warnings = warnings;
     let mut fresh = cached.clone();
     let mut calc = Calc::new();
     calc.recalc_all(&mut fresh);
@@ -1600,6 +1601,15 @@ mod tests {
         assert_eq!(package_of(&source), ["lost relationship madeUp"]);
     }
 
+    #[test]
+    fn json_lists_warning_messages() {
+        let with = FileReport { path: "a.ods".into(), warnings: vec!["ODS data-only import".into()], ..Default::default() };
+        let without = FileReport { path: "b.xlsx".into(), ..Default::default() };
+        let v = report_json(&[with, without], &Options::default());
+        assert_eq!(v["files"][0]["warnings"], json!(["ODS data-only import"]));
+        assert_eq!(v["files"][1]["warnings"], json!([]));
+    }
+
     #[test]
     fn unopenable_files_are_reported() {
         let r = check_bytes("broken.xlsx", b"PK\x03\x04 not really", &Options::default());