diff --git a/src/data/allvars.h b/src/data/allvars.h
index 122fd03757dd58b41709b7f63d4accc60a11ffd4..4270aed5c66ec42f2667a8001272433047a07173 100644
--- a/src/data/allvars.h
+++ b/src/data/allvars.h
@@ -24,11 +24,16 @@
 #include "../io/parameters.h"
 
 #ifdef MHD
+
+#ifndef MAGNETIC_SIGNALVEL
 #define MAGNETIC_SIGNALVEL
+#endif
+
 #ifndef DIVBFORCE 
 #define DIVBFORCE 1
 #endif
-#endif
+
+#endif //MHD
 
 /** Data which is the SAME for all tasks (mostly code parameters read
  * from the parameter file).  Holding this data in a structure is