diff --git a/ext/phar/phar.c b/ext/phar/phar.c
index b7becf27e32..51b28ec2b74 100644
--- a/ext/phar/phar.c
+++ b/ext/phar/phar.c
@@ -1719,7 +1719,7 @@ static zend_result phar_open_from_fp(php_stream* fp, char *fname, size_t fname_l
 			}
 
 			if (got >= 512) {
-				if (phar_is_tar((char *) pos, fname)) { /* TODO: fix const correctness */
+				if (phar_is_tar(pos, fname)) {
 					php_stream_rewind(fp);
 					return phar_parse_tarfile(fp, fname, fname_len, alias, alias_len, pphar, compression, error);
 				}
diff --git a/ext/phar/phar_internal.h b/ext/phar/phar_internal.h
index bd3d7158c8e..5acb0873ebd 100644
--- a/ext/phar/phar_internal.h
+++ b/ext/phar/phar_internal.h
@@ -443,7 +443,7 @@ zend_result phar_open_archive_fp(phar_archive_data *phar);
 zend_result phar_copy_on_write(phar_archive_data **pphar);
 
 /* tar functions in tar.c */
-bool phar_is_tar(char *buf, char *fname);
+bool phar_is_tar(const char *buf, const char *fname);
 zend_result phar_parse_tarfile(php_stream* fp, char *fname, size_t fname_len, char *alias, size_t alias_len, phar_archive_data** pphar, uint32_t compression, char **error);
 ZEND_ATTRIBUTE_NONNULL_ARGS(1, 7, 8) zend_result phar_open_or_create_tar(char *fname, size_t fname_len, char *alias, size_t alias_len, bool is_data, uint32_t options, phar_archive_data** pphar, char **error);
 ZEND_ATTRIBUTE_NONNULL_ARGS(1, 4) void phar_tar_flush(phar_archive_data *phar, zend_string *user_stub, bool is_default_stub, char **error);
diff --git a/ext/phar/tar.c b/ext/phar/tar.c
index 4847597cce2..67994289d0a 100644
--- a/ext/phar/tar.c
+++ b/ext/phar/tar.c
@@ -87,10 +87,10 @@ static zend_result phar_tar_octal(char *buf, uint32_t val, size_t len) /* {{{ */
 }
 /* }}} */
 
-static uint32_t phar_tar_checksum(char *buf, size_t len) /* {{{ */
+static uint32_t phar_tar_checksum(const char *buf, size_t len) /* {{{ */
 {
 	uint32_t sum = 0;
-	char *end = buf + len;
+	const char *end = buf + len;
 
 	while (buf != end) {
 		sum += (unsigned char)*buf;
@@ -100,7 +100,7 @@ static uint32_t phar_tar_checksum(char *buf, size_t len) /* {{{ */
 }
 /* }}} */
 
-bool phar_is_tar(char *buf, char *fname) /* {{{ */
+bool phar_is_tar(const char *buf, const char *fname) /* {{{ */
 {
 	tar_header *header = (tar_header *) buf;
 	uint32_t checksum = phar_tar_number(header->checksum, sizeof(header->checksum));