diff --git a/NEWS b/NEWS
index edd2429a3407..c715f4578a5f 100644
--- a/NEWS
+++ b/NEWS
@@ -199,6 +199,8 @@ PHP                                                                        NEWS
 - Phar:
   . Fixed bug GH-24740 (Oversized tar metadata exhausts the memory limit).
     (Lazizbek Ergashev)
+  . Fixed bug GH-8469 (Phar Class decompressFiles() bad in PHP 7.4 and 8.x
+    branches). (Raphael Paez)
 
 - Phpdbg:
   . Fix wrong command names. (ndossche, Weilin Du)
diff --git a/ext/phar/phar_object.c b/ext/phar/phar_object.c
index a1736f221e27..79ea1cf2df98 100644
--- a/ext/phar/phar_object.c
+++ b/ext/phar/phar_object.c
@@ -3173,6 +3173,30 @@ static int phar_set_compression(zval *zv, void *argument) /* {{{ */
 }
 /* }}} */
 
+typedef struct {
+	uint32_t compress;
+	char *error;
+} phar_compression_args;
+
+static int phar_decompress_for_compression_change(zval *zv, void *argument) /* {{{ */
+{
+	phar_entry_info *entry = (phar_entry_info *)Z_PTR_P(zv);
+	phar_compression_args *args = (phar_compression_args *)argument;
+	uint32_t current = entry->flags & PHAR_ENT_COMPRESSION_MASK;
+
+	if (entry->is_deleted || entry->is_dir || !current || current == args->compress) {
+		return ZEND_HASH_APPLY_KEEP;
+	}
+
+	/* phar_flush() would otherwise copy the old compressed bytes as the new contents */
+	if (FAILURE == phar_open_entry_fp(entry, &args->error, 0)) {
+		return ZEND_HASH_APPLY_STOP;
+	}
+
+	return ZEND_HASH_APPLY_KEEP;
+}
+/* }}} */
+
 static int phar_test_compression(zval *zv, void *argument) /* {{{ */
 {
 	phar_entry_info *entry = (phar_entry_info *)Z_PTR_P(zv);
@@ -3197,9 +3221,18 @@ static int phar_test_compression(zval *zv, void *argument) /* {{{ */
 }
 /* }}} */
 
-static void pharobj_set_compression(HashTable *manifest, uint32_t compress) /* {{{ */
+static zend_result pharobj_set_compression(HashTable *manifest, uint32_t compress, char **error) /* {{{ */
 {
+	phar_compression_args args = { .compress = compress, .error = NULL };
+
+	zend_hash_apply_with_argument(manifest, phar_decompress_for_compression_change, &args);
+	if (args.error) {
+		*error = args.error;
+		return FAILURE;
+	}
+
 	zend_hash_apply_with_argument(manifest, phar_set_compression, &compress);
+	return SUCCESS;
 }
 /* }}} */
 
@@ -3390,7 +3423,11 @@ PHP_METHOD(Phar, compressFiles)
 		zend_throw_exception_ex(phar_ce_PharException, 0, "phar \"%s\" is persistent, unable to copy on write", phar_obj->archive->fname);
 		RETURN_THROWS();
 	}
-	pharobj_set_compression(&phar_obj->archive->manifest, flags);
+	if (FAILURE == pharobj_set_compression(&phar_obj->archive->manifest, flags, &error)) {
+		zend_throw_exception_ex(spl_ce_BadMethodCallException, 0, "%s", error);
+		efree(error);
+		RETURN_THROWS();
+	}
 	phar_obj->archive->is_modified = 1;
 	phar_flush(phar_obj->archive, &error);
 
@@ -3432,7 +3469,11 @@ PHP_METHOD(Phar, decompressFiles)
 			zend_throw_exception_ex(phar_ce_PharException, 0, "phar \"%s\" is persistent, unable to copy on write", phar_obj->archive->fname);
 			RETURN_THROWS();
 		}
-		pharobj_set_compression(&phar_obj->archive->manifest, PHAR_ENT_COMPRESSED_NONE);
+		if (FAILURE == pharobj_set_compression(&phar_obj->archive->manifest, PHAR_ENT_COMPRESSED_NONE, &error)) {
+			zend_throw_exception_ex(spl_ce_BadMethodCallException, 0, "%s", error);
+			efree(error);
+			RETURN_THROWS();
+		}
 	}
 
 	phar_obj->archive->is_modified = 1;
diff --git a/ext/phar/tests/gh8469.phpt b/ext/phar/tests/gh8469.phpt
new file mode 100644
index 000000000000..ca34dca256cc
--- /dev/null
+++ b/ext/phar/tests/gh8469.phpt
@@ -0,0 +1,59 @@
+--TEST--
+GH-8469 (Phar::decompressFiles() and Phar::compressFiles() keep the old compressed contents)
+--EXTENSIONS--
+phar
+zlib
+bz2
+--INI--
+phar.require_hash=0
+phar.readonly=0
+--FILE--
+<?php
+$contents = str_repeat('four score and seven years ago ', 10);
+
+foreach (['phar', 'phar.zip'] as $ext) {
+    $fname = __DIR__ . "/gh8469.$ext";
+    $phar = new Phar($fname);
+    $phar['a.txt'] = $contents;
+    $phar['b.txt'] = 'our fathers';
+    $phar->addEmptyDir('dir');
+
+    $phar->compressFiles(Phar::GZ);
+    $phar->compressFiles(Phar::BZ2);
+    var_dump($phar['a.txt']->isCompressed(Phar::BZ2));
+    var_dump($phar['a.txt']->getContent() === $contents);
+
+    var_dump($phar->decompressFiles());
+    var_dump($phar['a.txt']->isCompressed());
+    var_dump($phar['a.txt']->getContent() === $contents);
+    var_dump($phar['b.txt']->getContent());
+    unset($phar);
+
+    $phar = new Phar($fname);
+    var_dump($phar['a.txt']->getContent() === $contents);
+    var_dump(file_get_contents("phar://$fname/b.txt"));
+    unset($phar);
+}
+?>
+--CLEAN--
+<?php
+@unlink(__DIR__ . '/gh8469.phar');
+@unlink(__DIR__ . '/gh8469.phar.zip');
+?>
+--EXPECT--
+bool(true)
+bool(true)
+bool(true)
+bool(false)
+bool(true)
+string(11) "our fathers"
+bool(true)
+string(11) "our fathers"
+bool(true)
+bool(true)
+bool(true)
+bool(false)
+bool(true)
+string(11) "our fathers"
+bool(true)
+string(11) "our fathers"