diff --git a/ext/iconv/iconv.c b/ext/iconv/iconv.c
index 13dc7074b9b3..b749907dc3e1 100644
--- a/ext/iconv/iconv.c
+++ b/ext/iconv/iconv.c
@@ -942,6 +942,8 @@ static php_iconv_err_t _php_iconv_mime_encode(smart_str *pretval, const char *fn
 		goto out;
 	}
 
+	buf = safe_emalloc(1, max_line_len, 5);
+
 	cd_pl = iconv_open(ICONV_ASCII_ENCODING, enc);
 	if (cd_pl == (iconv_t)(-1)) {
 		if (errno == EINVAL) {
@@ -962,8 +964,6 @@ static php_iconv_err_t _php_iconv_mime_encode(smart_str *pretval, const char *fn
 		goto out;
 	}
 
-	buf = safe_emalloc(1, max_line_len, 5);
-
 	char_cnt = max_line_len;
 
 	_php_iconv_appendl(pretval, fname, fname_nbytes, cd_pl);
diff --git a/ext/iconv/tests/gh17399.phpt b/ext/iconv/tests/gh17399.phpt
new file mode 100644
index 000000000000..078bfe2c39ce
--- /dev/null
+++ b/ext/iconv/tests/gh17399.phpt
@@ -0,0 +1,13 @@
+--TEST--
+GH-17399 (iconv memory leak with large line-length in iconv_mime_encode)
+--EXTENSIONS--
+iconv
+--FILE--
+<?php
+$options = array(
+    'line-length' => PHP_INT_MAX,
+);
+iconv_mime_encode('Subject', 'test', $options);
+?>
+--EXPECTF--
+Fatal error: Allowed memory size of %d bytes exhausted %s in %s on line %d