diff --git a/src/PVE/APIServer/AnyEvent.pm b/src/PVE/APIServer/AnyEvent.pm
index 915d678..bb49a8f 100644
--- a/src/PVE/APIServer/AnyEvent.pm
+++ b/src/PVE/APIServer/AnyEvent.pm
@@ -1382,8 +1382,9 @@ sub parse_content_type {
     my ($ct, @params) = split(/\s*[;,]\s*/o, $ctype);
 
     foreach my $v (@params) {
-        if ($v =~ m/^\s*boundary\s*=\s*(\S+?)\s*$/o) {
-            return wantarray ? ($ct, $1) : $ct;
+        # the boundary may be given as quoted-string, see RFC 2046, section 5.1.1
+        if ($v =~ m/^\s*boundary\s*=\s*(?:"([^"]+)"|(\S+?))\s*$/o) {
+            return wantarray ? ($ct, $1 // $2) : $ct;
         }
     }