diff --git a/crates/engine/src/cmd/insert.rs b/crates/engine/src/cmd/insert.rs
index e4b5bc9d1..b922b4c25 100644
--- a/crates/engine/src/cmd/insert.rs
+++ b/crates/engine/src/cmd/insert.rs
@@ -654,14 +654,16 @@ fn chart_switch(s: &mut Session, p: &Json) -> Result<Json> {
     edit(s, |cx| {
         let Some(sh) = cx.wb.sheet(si) else { return Ok(Json::Null) };
         let Some(c) = sh.charts.get(ci) else { return Ok(Json::Null) };
-        let Some(src) = c.source.clone() else { return Ok(Json::Null) };
+        // Charts read from a file have no source range: take the block their series span.
+        let Some((src, by_rows)) = c.source.clone().map(|s| (s, c.by_rows)).or_else(|| series_block(&c.series)) else { return Ok(Json::Null) };
         let (sheet_name, body) = split_sheet(&src);
         let src_sheet = sheet_name.and_then(|n| cx.wb.sheet_index(&n)).unwrap_or(si);
         let Some(r) = RangeRef::parse(body) else { return Ok(Json::Null) };
         let Some(ssh) = cx.wb.sheet(src_sheet) else { return Ok(Json::Null) };
-        let by_rows = !c.by_rows;
+        let by_rows = !by_rows;
         let series = series_from_range(ssh, r, by_rows);
         if let Some(c) = cx.sheet_mut(si)?.charts.get_mut(ci) {
+            c.source.get_or_insert(src);
             c.by_rows = by_rows;
             c.series = series;
         }
@@ -669,6 +671,29 @@ fn chart_switch(s: &mut Session, p: &Json) -> Result<Json> {
     })
 }
 
+/// The block a chart's series come from, and whether each series is a row of it: the bounding
+/// range of the series names, categories and values, when they're all references to one sheet.
+fn series_block(series: &[Series]) -> Option<(String, bool)> {
+    let mut sheet: Option<String> = None;
+    let mut bounds: Option<RangeRef> = None;
+    let mut rows = 0;
+    for s in series {
+        for (i, f) in [Some(&s.values), s.categories.as_ref(), s.name.as_ref()].into_iter().flatten().enumerate() {
+            let Ok(gridcraft_formula::Expr::Ref(r)) = gridcraft_formula::parse(f) else { return None };
+            let gridcraft_formula::SheetSel::Named(n) = &r.sheet else { return None };
+            if !sheet.get_or_insert_with(|| n.clone()).eq_ignore_ascii_case(n) {
+                return None;
+            }
+            let range = r.range();
+            if i == 0 && range.height() == 1 && range.width() > 1 {
+                rows += 1;
+            }
+            bounds = Some(bounds.map_or(range, |b| b.union(&range)));
+        }
+    }
+    Some((format!("{}!{}", gridcraft_formula::quote_sheet(&sheet?), bounds?.a1()), rows > 0 && rows == series.len()))
+}
+
 fn chart_delete(s: &mut Session, p: &Json) -> Result<Json> {
     let (si, ci) = find_chart(s, p)?;
     edit(s, |cx| {
diff --git a/crates/engine/src/tests.rs b/crates/engine/src/tests.rs
index f3e36cdf4..6a01542ed 100644
--- a/crates/engine/src/tests.rs
+++ b/crates/engine/src/tests.rs
@@ -174,6 +174,32 @@ fn parity_counts() {
     assert!(done > 150, "parity {done}/{total}");
 }
 
+#[test]
+fn switch_row_column_on_a_chart_read_from_a_file() {
+    let mut s = s();
+    s.execute(
+        "range.setValues",
+        json!({"range": "A1", "values": [["", "North", "South", "East", "West"], ["Mon", 10, 14, 9, 12], ["Tue", 12, 15, 11, 14], ["Wed", 14, 16, 10, 11], ["Thu", 11, 13, 8, 9], ["Fri", 9, 12, 7, 11], ["Sat", 11, 15, 10, 14]]}),
+    )
+    .unwrap();
+    s.execute("insert.chart", json!({"type": "column", "range": "A1:E7"})).unwrap();
+    let r = s.execute("file.saveBytes", json!({"format": "xlsx"})).unwrap();
+    let b64 = r["base64"].as_str().unwrap().to_string();
+    s.execute("file.open", json!({"name": "x.xlsx", "base64": b64})).unwrap();
+    let chart = |s: &Session| s.doc().unwrap().wb.active().unwrap().charts[0].clone();
+    assert_eq!((chart(&s).source, chart(&s).series.len()), (None, 4));
+    s.execute("chart.switchRowColumn", json!({})).unwrap();
+    let c = chart(&s);
+    assert!(c.by_rows);
+    assert_eq!(c.source.as_deref(), Some("Sheet1!A1:E7"));
+    assert_eq!(c.series.len(), 6);
+    assert_eq!(c.series[0].name.as_deref(), Some("Sheet1!$A$2"));
+    assert_eq!(c.series[0].categories.as_deref(), Some("Sheet1!$B$1:$E$1"));
+    assert_eq!(c.series[0].values, "Sheet1!$B$2:$E$2");
+    s.execute("chart.switchRowColumn", json!({})).unwrap();
+    assert_eq!(chart(&s).series.len(), 4);
+}
+
 #[test]
 fn ink_strokes_and_ink_to_shape() {
     let mut s = s();