diff --git a/simgear/debug/debug_types.h b/simgear/debug/debug_types.h
index 2443276b..cc856556 100644
--- a/simgear/debug/debug_types.h
+++ b/simgear/debug/debug_types.h
@@ -34,7 +34,8 @@ typedef enum {
     SG_GUI         = 0x00800000,
     SG_TERRASYNC   = 0x01000000,
     SG_PARTICLES   = 0x02000000,
-    SG_UNDEFD      = 0x04000000, // For range checking
+    SG_HEADLESS    = 0x04000000,
+    SG_UNDEFD      = 0x08000000, // For range checking
 
     SG_ALL         = 0xFFFFFFFF
 } sgDebugClass;
diff --git a/simgear/debug/logstream.cxx b/simgear/debug/logstream.cxx
index b8b4d312..4e2f6ee4 100644
--- a/simgear/debug/logstream.cxx
+++ b/simgear/debug/logstream.cxx
@@ -100,6 +100,7 @@ const char* LogCallback::debugClassToString(sgDebugClass c)
         case SG_GUI:        return "gui";
         case SG_TERRASYNC:  return "terrasync";
         case SG_PARTICLES:  return "particles";
+        case SG_HEADLESS:   return "headless";
         default:            return "unknown";
     }
 }