diff --git a/NEWS b/NEWS
index 6943db07f6a..56eed2700a7 100644
--- a/NEWS
+++ b/NEWS
@@ -24,6 +24,9 @@ PHP                                                                        NEWS
   . Fixed bug #80368 (OpenSSL extension fails to build against LibreSSL due to
     lack of OCB support). (Nikita)
 
+- Phar:
+  . Fixed bug #73809 (Phar Zip parse crash - mmap fail). (cmb)
+
 - Phpdbg:
   . Fixed bug #76813 (Access violation near NULL on source operand). (cmb)
 
diff --git a/ext/phar/tests/bug73809.phpt b/ext/phar/tests/bug73809.phpt
new file mode 100644
index 00000000000..5356db8aaa0
--- /dev/null
+++ b/ext/phar/tests/bug73809.phpt
@@ -0,0 +1,30 @@
+--TEST--
+Bug #73809 (Phar Zip parse crash - mmap fail)
+--SKIPIF--
+<?php
+if (!extension_loaded('phar')) die('skip phar extension not available');
+if (!extension_loaded('zip')) die('skip zip extension not available');
+?>
+--FILE--
+<?php
+// create the ZIP to be tested
+$zip = new ZipArchive;
+$zip->open(__DIR__ . '/73809.zip', ZipArchive::CREATE);
+$zip->addFromString('73809.txt', 'yada yada');
+$zip->addFromString('.phar/signature.bin', str_repeat('*', 64 * 1024 + 1));
+$zip->setCompressionName('.phar/signature.bin', ZipArchive::CM_STORE);
+var_dump($zip->close());
+
+try {
+    $phar = new PharData(__DIR__ . '/73809.zip');
+} catch (Exception $ex) {
+    echo $ex->getMessage(), PHP_EOL;
+}
+?>
+--CLEAN--
+<?php
+@unlink(__DIR__ . '/73809.zip');
+?>
+--EXPECTF--
+bool(true)
+phar error: signatures larger than 64 KiB are not supported in zip-based phar "%s"
diff --git a/ext/phar/zip.c b/ext/phar/zip.c
index b241c0589b4..0bf873aff16 100644
--- a/ext/phar/zip.c
+++ b/ext/phar/zip.c
@@ -405,8 +405,13 @@ foundit:
 			char *sig;
 			size_t sig_len;
 
-			php_stream_tell(fp);
 			pefree(entry.filename, entry.is_persistent);
+
+			if (entry.uncompressed_filesize > 0x10000) {
+				PHAR_ZIP_FAIL("signatures larger than 64 KiB are not supported");
+			}
+
+			php_stream_tell(fp);
 			sigfile = php_stream_fopen_tmpfile();
 			if (!sigfile) {
 				PHAR_ZIP_FAIL("couldn't open temporary file");