diff --git a/src/generics/lib.generics.ts b/src/generics/lib.generics.ts
index dc097f4..0160db3 100644
--- a/src/generics/lib.generics.ts
+++ b/src/generics/lib.generics.ts
@@ -577,9 +577,10 @@ namespace __Array {
     function flatMap<T, V>(this: T[], func: (v: T, i: number) => V[]): V[] {
         const result: V[] = [];
         for (let i = 0; i < this.length; i++) {
-            // moved out of the array func made, which goes when this loop turns
+            // read, as flat reads: func may give an array it holds on to (the same one for every
+            // element, a row of a table), so nothing is moved out of it
             const mapped = func(this[i], i);
-            __moveAll(mapped, result);
+            for (const v of mapped) result.push(v);
         }
 
         return result;
diff --git a/tests/array_flatMap_shared.ts b/tests/array_flatMap_shared.ts
new file mode 100644
index 0000000..f78c025
--- /dev/null
+++ b/tests/array_flatMap_shared.ts
@@ -0,0 +1,25 @@
+// not own: a callback there cannot return an array it does not own ("borrows a captured variable")
+// flatMap reads the array its callback gives: one the callback did not make is left as it was.
+function main() {
+    const ones: number[] = [1, 2, 3];
+
+    // the same array for every element
+    const pair: number[] = [7, 8];
+    const repeated = ones.flatMap((v: number, i: number) => pair);
+    assert(repeated.join(",") == "7,8,7,8,7,8", "flatMap of one array given three times");
+    assert(pair.length == 2 && pair.join(",") == "7,8", "flatMap leaves the array it was given");
+
+    // rows of a table
+    const rows: string[][] = [["a", "b"], ["c"]];
+    const cells = [1, 0, 1].flatMap((v: number, i: number) => rows[v]);
+    assert(cells.join(",") == "c,a,b,c", "flatMap of arrays held elsewhere");
+    assert(rows[0].length == 2 && rows[1].length == 1, "which stay as they were");
+
+    // the Array<T> class
+    const a = new Array<number>();
+    a.push(1, 2);
+    assert(a.flatMap((v: number, i: number) => pair).join(",") == "7,8,7,8", "Array<T>.flatMap");
+    assert(pair.length == 2, "Array<T>.flatMap leaves it too");
+
+    console.log("ALL DONE");
+}