diff --git a/ext/standard/tests/file/gh13136.phpt b/ext/standard/tests/file/gh13136.phpt
new file mode 100644
index 0000000000000..a90c07c91c280
--- /dev/null
+++ b/ext/standard/tests/file/gh13136.phpt
@@ -0,0 +1,55 @@
+--TEST--
+GH-13071 (Copying large files using mmap-able source streams may exhaust available memory and fail)
+--FILE--
+<?php
+
+class CustomStream {
+    public $context;
+    protected $file;
+    protected $seekable;
+    public static int $writes = 0;
+
+    public function stream_open($path, $mode, $options, &$opened_path) {
+        $path = $this->trim_path($path);
+        $this->file = fopen($path, $mode);
+        return true;
+    }
+
+    public function stream_close() {
+        fclose($this->file);
+        return true;
+    }
+
+    public function stream_write($data) {
+        self::$writes++;
+        return fwrite($this->file, $data);
+    }
+
+    public function url_stat($path, $flags) {
+        return false;
+    }
+
+    private function trim_path(string $path): string {
+        return substr($path, strlen("up://"));
+    }
+}
+
+file_put_contents(__DIR__ . "/gh13071.tmp", str_repeat("a", 1024 * 1024 * 8));
+
+stream_wrapper_register("up", CustomStream::class, STREAM_IS_URL);
+
+$old_limit = ini_get("memory_limit");
+ini_set("memory_limit", memory_get_usage(true) + 5 * 1024 * 1024);
+copy(__DIR__ . "/gh13071.tmp", "up://" . __DIR__ . "/gh13071.out.tmp");
+ini_set("memory_limit", $old_limit);
+
+echo "Done ", CustomStream::$writes, " writes\n";
+
+?>
+--CLEAN--
+<?php
+@unlink(__DIR__ . "/gh13071.tmp");
+@unlink(__DIR__ . "/gh13071.out.tmp");
+?>
+--EXPECT--
+Done 1024 writes
diff --git a/ext/standard/tests/file/userstreams_006.phpt b/ext/standard/tests/file/userstreams_006.phpt
index a432937dac29f..e5d341379f6d1 100644
--- a/ext/standard/tests/file/userstreams_006.phpt
+++ b/ext/standard/tests/file/userstreams_006.phpt
@@ -34,5 +34,6 @@ bool(true)
 option: 3, 2, 50
 int(-1)
 int(8192)
-size: 70
+size: 42
+size: 28
 int(70)
diff --git a/ext/standard/tests/streams/set_file_buffer.phpt b/ext/standard/tests/streams/set_file_buffer.phpt
index ef808a24fd002..c39ba56cf6cfb 100644
--- a/ext/standard/tests/streams/set_file_buffer.phpt
+++ b/ext/standard/tests/streams/set_file_buffer.phpt
@@ -39,4 +39,5 @@ option: %d, %d, %d
 int(%i)
 int(%d)
 size: %d
+size: 28
 int(%d)
diff --git a/ext/standard/tests/streams/stream_set_chunk_size.phpt b/ext/standard/tests/streams/stream_set_chunk_size.phpt
index 77d9bac00ea4f..8bb5b46b7f94a 100644
--- a/ext/standard/tests/streams/stream_set_chunk_size.phpt
+++ b/ext/standard/tests/streams/stream_set_chunk_size.phpt
@@ -35,7 +35,7 @@ echo "should return previous chunk size (8192)\n";
 var_dump(stream_set_chunk_size($f, 1));
 echo "should be read without buffer (\$count == 10000)\n";
 var_dump(strlen(fread($f, 10000)));
-echo "should have no effect on writes\n";
+echo "should elicit 3 writes\n";
 var_dump(fwrite($f, str_repeat('b', 3)));
 
 echo "should return previous chunk size (1)\n";
@@ -46,7 +46,7 @@ echo "should elicit one read of size 100 (chunk size)\n";
 var_dump(strlen(fread($f, 50)));
 echo "should elicit no read because there is sufficient cached data\n";
 var_dump(strlen(fread($f, 50)));
-echo "should have no effect on writes\n";
+echo "should elicit 3 writes\n";
 var_dump(strlen(fwrite($f, str_repeat('b', 250))));
 
 echo "\nerror conditions\n";
@@ -68,8 +68,10 @@ int(8192)
 should be read without buffer ($count == 10000)
 read with size: 10000
 int(10000)
-should have no effect on writes
-write with size: 3
+should elicit 3 writes
+write with size: 1
+write with size: 1
+write with size: 1
 int(3)
 should return previous chunk size (1)
 int(1)
@@ -81,8 +83,10 @@ read with size: 100
 int(50)
 should elicit no read because there is sufficient cached data
 int(50)
-should have no effect on writes
-write with size: 250
+should elicit 3 writes
+write with size: 100
+write with size: 100
+write with size: 50
 int(3)
 
 error conditions
diff --git a/main/streams/streams.c b/main/streams/streams.c
index e1399927b2783..d45a9bfab85f8 100644
--- a/main/streams/streams.c
+++ b/main/streams/streams.c
@@ -1133,8 +1133,15 @@ static ssize_t _php_stream_write_buffer(php_stream *stream, const char *buf, siz
 		stream->ops->seek(stream, stream->position, SEEK_SET, &stream->position);
 	}
 
+	/* See GH-13071: userspace stream is subject to the memory limit. */
+	size_t chunk_size = count;
+	if (php_stream_is(stream, PHP_STREAM_IS_USERSPACE)) {
+		/* If the stream is unbuffered, we can only write one byte at a time. */
+		chunk_size = stream->chunk_size;
+	}
+
 	while (count > 0) {
-		ssize_t justwrote = stream->ops->write(stream, buf, count);
+		ssize_t justwrote = stream->ops->write(stream, buf, MIN(chunk_size, count));
 		if (justwrote <= 0) {
 			/* If we already successfully wrote some bytes and a write error occurred
 			 * later, report the successfully written bytes. */