diff --git a/scp.h b/scp.h
index 3e2b1435..9b511a43 100644
--- a/scp.h
+++ b/scp.h
@@ -333,7 +333,7 @@ void sim_debug_bits (uint32 dbits, DEVICE* dptr, BITFIELD* bitdefs,
 #define _sim_debug_device sim_debug
 void sim_debug (uint32 dbits, DEVICE* dptr, const char *fmt, ...) GCC_FMT_ATTR(3, 4);
 #define _sim_debug_unit sim_debug_unit
-void sim_debug_unit (uint32 dbits, DEVICE* dptr, const char *fmt, ...) GCC_FMT_ATTR(3, 4);
+void sim_debug_unit (uint32 dbits, UNIT* uptr, const char *fmt, ...) GCC_FMT_ATTR(3, 4);
 #else
 void _sim_debug_unit (uint32 dbits, UNIT *uptr, const char* fmt, ...) GCC_FMT_ATTR(3, 4);
 void _sim_debug_device (uint32 dbits, DEVICE* dptr, const char* fmt, ...) GCC_FMT_ATTR(3, 4);