diff --git a/src/PVE/JSONSchema.pm b/src/PVE/JSONSchema.pm
index 34f2949..0686b67 100644
--- a/src/PVE/JSONSchema.pm
+++ b/src/PVE/JSONSchema.pm
@@ -256,7 +256,8 @@ sub pve_verify_configid {
 
     if ($id !~ m/^$CONFIGID_RE\z/) {
         return undef if $noerr;
-        die "invalid configuration ID '$id'\n";
+        die "invalid configuration ID '$id' - it must start with a letter, be at least two"
+            . " characters long and only contain letters, digits, '-' and '_'\n";
     }
     return $id;
 }
diff --git a/test/format_test.pl b/test/format_test.pl
index 7b461ef..46256f4 100644
--- a/test/format_test.pl
+++ b/test/format_test.pl
@@ -25,6 +25,14 @@ foreach my $id (@$invalid_configids) {
     is(PVE::JSONSchema::pve_verify_configid($id, $noerr), undef, 'invalid configid');
 }
 
+eval { PVE::JSONSchema::pve_verify_configid('gpu@node1') };
+is(
+    $@,
+    "invalid configuration ID 'gpu\@node1' - it must start with a letter, be at least two"
+        . " characters long and only contain letters, digits, '-' and '_'\n",
+    'invalid configid error explains the format',
+);
+
 # test some string rendering
 my $render_data = [
     ["timestamp", 0, undef, "1970-01-01 01:00:00"],