diff --git a/src/aggregate.zig b/src/aggregate.zig
index d8db1b9..5165378 100644
--- a/src/aggregate.zig
+++ b/src/aggregate.zig
@@ -810,3 +810,164 @@ test "count_distinct on zero observed values reports zero, not none" {
     try std.testing.expectEqual(@as(i64, 0), values[0].int);
 }
 
+test "count_distinct propagates OutOfMemory without leaking already-tracked distinct values" {
+    const allocator = std.testing.allocator;
+    var rows = std.ArrayList(Row).init(allocator);
+    defer {
+        for (rows.items) |*r| r.deinit();
+        rows.deinit();
+    }
+    const tags = [_][]const u8{ "red", "blue", "green" };
+    for (tags) |t| {
+        try rows.append(try makeRow(allocator, &.{
+            .{ .name = "g", .value = .{ .text = "x" } },
+            .{ .name = "tag", .value = .{ .text = t } },
+        }));
+    }
+
+    var failing = std.testing.FailingAllocator.init(allocator, .{ .fail_index = 6 });
+    const specs = [_]AggSpec{.{ .field = "tag", .kind = .count_distinct }};
+    var gb = GroupBy.init(failing.allocator(), "g", &specs);
+    defer gb.deinit();
+
+    var sawError = false;
+    for (rows.items) |*r| {
+        gb.observe(r) catch {
+            sawError = true;
+            break;
+        };
+    }
+    try std.testing.expect(sawError);
+}
+
+test "rows missing the group field are excluded from every group" {
+    const allocator = std.testing.allocator;
+    var rows = std.ArrayList(Row).init(allocator);
+    defer {
+        for (rows.items) |*r| r.deinit();
+        rows.deinit();
+    }
+    try rows.append(try makeRow(allocator, &.{.{ .name = "team", .value = .{ .text = "a" } }}));
+    try rows.append(try makeRow(allocator, &.{})); // no "team" field at all
+
+    const specs = [_]AggSpec{.{ .field = "", .kind = .count }};
+    const groups = try run(allocator, rows.items, "team", &specs);
+    defer freeGroupRows(allocator, groups);
+
+    try std.testing.expectEqual(@as(usize, 1), groups.len);
+    try std.testing.expectEqual(@as(i64, 1), groups[0].values[0].int);
+}
+
+test "group order is first-seen, not sorted" {
+    const allocator = std.testing.allocator;
+    var rows = std.ArrayList(Row).init(allocator);
+    defer {
+        for (rows.items) |*r| r.deinit();
+        rows.deinit();
+    }
+    const order = [_][]const u8{ "z", "a", "m" };
+    for (order) |g| {
+        try rows.append(try makeRow(allocator, &.{.{ .name = "g", .value = .{ .text = g } }}));
+    }
+
+    const specs = [_]AggSpec{.{ .field = "", .kind = .count }};
+    const groups = try run(allocator, rows.items, "g", &specs);
+    defer freeGroupRows(allocator, groups);
+
+    try std.testing.expectEqual(@as(usize, 3), groups.len);
+    try std.testing.expectEqualStrings("z", groups[0].group.text);
+    try std.testing.expectEqualStrings("a", groups[1].group.text);
+    try std.testing.expectEqualStrings("m", groups[2].group.text);
+}
+
+test "runGlobal aggregates every row into a single result with no grouping" {
+    const allocator = std.testing.allocator;
+    var rows = std.ArrayList(Row).init(allocator);
+    defer {
+        for (rows.items) |*r| r.deinit();
+        rows.deinit();
+    }
+    var i: i64 = 1;
+    while (i <= 4) : (i += 1) {
+        try rows.append(try makeRow(allocator, &.{.{ .name = "x", .value = .{ .int = i } }}));
+    }
+
+    const specs = [_]AggSpec{
+        .{ .field = "", .kind = .count },
+        .{ .field = "x", .kind = .sum },
+        .{ .field = "x", .kind = .max },
+    };
+    const values = try runGlobal(allocator, rows.items, &specs);
+    defer freeGlobalResult(allocator, values);
+
+    try std.testing.expectEqual(@as(i64, 4), values[0].int);
+    try std.testing.expectEqual(@as(i64, 10), values[1].int);
+    try std.testing.expectEqual(@as(i64, 4), values[2].int);
+}
+
+test "runGlobal on zero rows still reports identity results, not an error" {
+    const allocator = std.testing.allocator;
+    const rows: []const Row = &.{};
+    const specs = [_]AggSpec{
+        .{ .field = "", .kind = .count },
+        .{ .field = "x", .kind = .sum },
+        .{ .field = "x", .kind = .max },
+    };
+    const values = try runGlobal(allocator, rows, &specs);
+    defer freeGlobalResult(allocator, values);
+
+    try std.testing.expectEqual(@as(i64, 0), values[0].int);
+    try std.testing.expectEqual(@as(i64, 0), values[1].int);
+    try std.testing.expectEqual(rowmod.ValueTag.none, @as(rowmod.ValueTag, values[2]));
+}
+
+test "GroupBy propagates OutOfMemory without leaking any accumulated group" {
+    const allocator = std.testing.allocator;
+    var rows = std.ArrayList(Row).init(allocator);
+    defer {
+        for (rows.items) |*r| r.deinit();
+        rows.deinit();
+    }
+    const groupNames = [_][]const u8{ "a", "b", "c" };
+    for (groupNames) |g| {
+        try rows.append(try makeRow(allocator, &.{
+            .{ .name = "g", .value = .{ .text = g } },
+            .{ .name = "x", .value = .{ .int = 1 } },
+        }));
+    }
+
+    var failing = std.testing.FailingAllocator.init(allocator, .{ .fail_index = 6 });
+    const specs = [_]AggSpec{.{ .field = "x", .kind = .sum }};
+    var gb = GroupBy.init(failing.allocator(), "g", &specs);
+    defer gb.deinit();
+
+    var sawError = false;
+    for (rows.items) |*r| {
+        gb.observe(r) catch {
+            sawError = true;
+            break;
+        };
+    }
+    try std.testing.expect(sawError);
+}
+
+fn fourGroupRows(allocator: Allocator) ![]GroupRow {
+    var rows = std.ArrayList(Row).init(allocator);
+    defer {
+        for (rows.items) |*r| r.deinit();
+        rows.deinit();
+    }
+    const groupNames = [_][]const u8{ "a", "b", "c", "d" };
+    for (groupNames) |g| {
+        try rows.append(try makeRow(allocator, &.{.{ .name = "g", .value = .{ .text = g } }}));
+    }
+    const specs = [_]AggSpec{.{ .field = "", .kind = .count }};
+    return run(allocator, rows.items, "g", &specs);
+}
+
+fn firstLettersOf(rows: []const GroupRow) [4]u8 {
+    var out: [4]u8 = undefined;
+    for (rows, 0..) |r, i| out[i] = r.group.text[0];
+    return out;
+}
+