diff --git a/program/lib/Roundcube/rcube_vcard.php b/program/lib/Roundcube/rcube_vcard.php
index 4d37e7dd01..f34fa75cfe 100644
--- a/program/lib/Roundcube/rcube_vcard.php
+++ b/program/lib/Roundcube/rcube_vcard.php
@@ -755,7 +755,7 @@ private static function vcard_decode($vcard)
                             $value = strtoupper($value);
                             // add next line(s) to value string if QP line end detected
                             if ($value == 'QUOTED-PRINTABLE') {
-                                while (preg_match('/=$/', $lines[$i])) {
+                                while (isset($lines[$i]) && preg_match('/=$/', $lines[$i]) && isset($lines[$i + 1])) {
                                     $data .= "\n" . $lines[++$i];
                                 }
                             }
@@ -1049,7 +1049,7 @@ private static function detect_encoding($string)
                 $enc = $matches ? strtoupper($matches[1]) : 'BASE64';
                 // add next line(s) to value string if QP line end detected
                 if ($enc == 'QUOTED-PRINTABLE') {
-                    while (preg_match('/=$/', $lines[$i])) {
+                    while (isset($lines[$i]) && preg_match('/=$/', $lines[$i]) && isset($lines[$i + 1])) {
                         $data .= "\n" . $lines[++$i];
                     }
                 }
diff --git a/tests/Framework/VCardTest.php b/tests/Framework/VCardTest.php
index acd5ea38f7..61ecaca2ea 100644
--- a/tests/Framework/VCardTest.php
+++ b/tests/Framework/VCardTest.php
@@ -102,6 +102,36 @@ public function test_parse_six()
         $this->assertCount(1, $result['address:work'], 'ITEM1.-prefixed entry');
     }
 
+    /**
+     * A QUOTED-PRINTABLE soft-line-break ('=') on the very last line must not
+     * cause reading past the end of the internal lines array.
+     */
+    public function test_parse_qp_soft_break_on_last_line()
+    {
+        $errors = [];
+        set_error_handler(static function ($errno, $errstr) use (&$errors) {
+            $errors[] = $errstr;
+
+            return true;
+        });
+
+        try {
+            // Last line ends with '=' (QP soft line break) with no following line
+            $vcard_string = "BEGIN:VCARD\r\n"
+                . "VERSION:3.0\r\n"
+                . "FN:Test\r\n"
+                . 'NOTE;ENCODING=QUOTED-PRINTABLE:Hello=';
+
+            $vcard = new \rcube_vcard($vcard_string, null, true);
+            $result = $vcard->get_assoc();
+        } finally {
+            restore_error_handler();
+        }
+
+        $this->assertSame([], $errors, 'No PHP warnings/errors while decoding');
+        $this->assertSame('Hello', $result['notes'][0], 'Best-effort QP decode of the dangling line');
+    }
+
     /**
      * Extra whitespace at start of continuation line (#9593/1).
      */