diff --git a/PVE/API2/Qemu.pm b/PVE/API2/Qemu.pm
index fb192760..bf1e1bb0 100644
--- a/PVE/API2/Qemu.pm
+++ b/PVE/API2/Qemu.pm
@@ -499,7 +499,8 @@ my sub create_disks : prototype($$$$$$$$$$$) {
 		} else {
 		    $source = PVE::Storage::abs_filesystem_path($storecfg, $source, 1);
 		    # check potentially untrusted image file!
-		    ($size, my $source_format) = PVE::Storage::file_size_info($source, undef, 1);
+		    ($size, my $source_format) =
+			PVE::Storage::file_size_info($source, undef, 'auto-detect', 1);
 		    die "could not get file size of $source\n" if !$size;
 
 		    if ($live_import && $ds ne 'efidisk0') {