diff --git a/src/emu/machine/rescap.h b/src/emu/machine/rescap.h
index db7e70e591e..afac4713f8c 100644
--- a/src/emu/machine/rescap.h
+++ b/src/emu/machine/rescap.h
@@ -2,6 +2,7 @@
 #define RC_MACROS_H
 
 /* Little helpers for magnitude conversions */
+#define RES_R(res) ((double)(res))
 #define RES_K(res) ((double)(res) * 1e3)
 #define RES_M(res) ((double)(res) * 1e6)
 #define CAP_U(cap) ((double)(cap) * 1e-6)