diff --git a/lib/std/Io/Writer.zig b/lib/std/Io/Writer.zig
index 5bb813913ae9b622e1ca9f30bd33ce87c1857a7d..813142a7a35e48c1de0eaba49bea2a5f47ec1139 100644
--- a/lib/std/Io/Writer.zig
+++ b/lib/std/Io/Writer.zig
@@ -802,12 +802,14 @@ pub fn splatBytePreserve(w: *Writer, preserve: usize, byte: u8, n: usize) Error!
             return;
         }
     }
-    // All the next bytes received must be preserved.
-    if (preserve < w.end) {
-        @memmove(w.buffer[0..preserve], w.buffer[w.end - preserve ..][0..preserve]);
-        w.end = preserve;
-    }
-    while (remaining > 0) remaining -= try w.splatByte(byte, remaining);
+    // Ensure the contract of `rebase` is upheld.
+    assert(w.end + remaining > w.buffer.len);
+    // Offset the amount preserved by the amount we have left to splat
+    // since the remaining splat is always going to be part of that
+    // preservation.
+    try w.vtable.rebase(w, preserve -| remaining, remaining);
+    @memset(w.buffer[w.end..][0..remaining], byte);
+    w.end += remaining;
 }
 
 /// Writes the same byte many times, allowing short writes.
@@ -2887,3 +2889,46 @@ test "writableSlice with fixed writer" {
     try w.writeByte(1);
     try std.testing.expectError(error.WriteFailed, w.writableSlice(2));
 }
+
+test splatBytePreserve {
+    try testSplatBytePreserve(.{ .buf_len = 10, .fill_len = 5, .preserve = 5, .splat_len = 5 });
+    try testSplatBytePreserve(.{ .buf_len = 10, .fill_len = 9, .preserve = 5, .splat_len = 2 });
+    try testSplatBytePreserve(.{ .buf_len = 10, .fill_len = 5, .preserve = 5, .splat_len = 6 });
+    try testSplatBytePreserve(.{ .buf_len = 10, .fill_len = 5, .preserve = 6, .splat_len = 6 });
+    try testSplatBytePreserve(.{ .buf_len = 10, .fill_len = 5, .preserve = 5, .splat_len = 10 });
+    try testSplatBytePreserve(.{ .buf_len = 10, .fill_len = 5, .preserve = 6, .splat_len = 10 });
+    try testSplatBytePreserve(.{ .buf_len = 10, .fill_len = 5, .preserve = 6, .splat_len = 11 });
+    try testSplatBytePreserve(.{ .buf_len = 10, .fill_len = 5, .preserve = 6, .splat_len = 80 });
+    try testSplatBytePreserve(.{ .buf_len = 10, .fill_len = 5, .preserve = 6, .splat_len = 85 });
+    try testSplatBytePreserve(.{ .buf_len = 10, .fill_len = 5, .preserve = 10, .splat_len = 6 });
+    try testSplatBytePreserve(.{ .buf_len = 10, .fill_len = 5, .preserve = 10, .splat_len = 11 });
+    try testSplatBytePreserve(.{ .buf_len = 10, .fill_len = 5, .preserve = 10, .splat_len = 80 });
+    try testSplatBytePreserve(.{ .buf_len = 10, .fill_len = 5, .preserve = 10, .splat_len = 85 });
+}
+
+fn testSplatBytePreserve(options: struct { buf_len: u4, fill_len: u4, preserve: u4, splat_len: u8 }) !void {
+    assert(options.fill_len <= options.buf_len);
+    assert(options.preserve <= options.buf_len);
+
+    const fill_buf = "abcdefghijklmno";
+    const fill = fill_buf[0..options.fill_len];
+    var expected_out_buf: [256]u8 = @splat('X');
+    @memcpy(expected_out_buf[0..options.fill_len], fill);
+    const expected_out = expected_out_buf[0 .. options.fill_len + options.splat_len];
+    const expected_preserved = expected_out[expected_out.len -| options.preserve..];
+
+    var out_buf: [256]u8 = undefined;
+    var fw: Writer = .fixed(&out_buf);
+    var indirect_buffer: [16]u8 = undefined;
+    var twi: std.testing.WriterIndirect = .init(&fw, indirect_buffer[0..options.buf_len]);
+    const w = &twi.interface;
+
+    try w.writeAll(fill);
+    try w.splatBytePreserve(options.preserve, 'X', options.splat_len);
+
+    try std.testing.expectEqualStrings(expected_preserved, w.buffer[w.end -| options.preserve..w.end]);
+
+    try w.flush();
+
+    try std.testing.expectEqualStrings(expected_out, fw.buffer[0..fw.end]);
+}
diff --git a/lib/std/testing.zig b/lib/std/testing.zig
index 57bddc49bb9efc0a7a5ea5082a77f2d3c0314e48..d262ca0c43a52c5364f405cc623b380c252d3915 100644
--- a/lib/std/testing.zig
+++ b/lib/std/testing.zig
@@ -1334,6 +1334,67 @@ pub const ReaderIndirect = struct {
     }
 };
 
+/// A `Io.Writer` that writes its data to another `Io.Writer`, and only
+/// writes new data to its own buffer during `drain`.
+pub const WriterIndirect = struct {
+    out: *Io.Writer,
+    interface: Io.Writer,
+
+    pub fn init(out: *Io.Writer, buffer: []u8) WriterIndirect {
+        return .{
+            .out = out,
+            .interface = .{
+                .vtable = &.{
+                    .drain = drain,
+                },
+                .buffer = buffer,
+                .end = 0,
+            },
+        };
+    }
+
+    fn drain(w: *Io.Writer, data: []const []const u8, splat: usize) std.Io.Writer.Error!usize {
+        const w_indirect: *WriterIndirect = @alignCast(@fieldParentPtr("interface", w));
+
+        // Write all data in the buffer to `out`
+        try w_indirect.out.writeAll(w.buffer[0..w.end]);
+        w.end = 0;
+
+        // Refill buffer using data
+        {
+            const end_before_fill = w.end;
+            for (data[0 .. data.len - 1]) |bytes| {
+                const dest = w.buffer[w.end..];
+                const len = @min(bytes.len, dest.len);
+                @memcpy(dest[0..len], bytes[0..len]);
+                w.end += len;
+            }
+            const pattern = data[data.len - 1];
+            switch (pattern.len) {
+                0 => {},
+                1 => {
+                    const len = @min(w.buffer[w.end..].len, splat);
+                    @memset(w.buffer[w.end..][0..len], pattern[0]);
+                    w.end += len;
+                },
+                else => {
+                    const dest = w.buffer[w.end..];
+                    for (0..splat) |i| {
+                        const start_i = i * pattern.len;
+                        if (start_i >= dest.len) break;
+                        const remaining = dest[start_i..];
+                        const len = @min(pattern.len, remaining.len);
+                        @memcpy(remaining[0..len], pattern[0..len]);
+                        w.end += len;
+                    }
+                },
+            }
+
+            return w.end - end_before_fill;
+        }
+    }
+};
+
 test {
     _ = &Smith;
 }