diff --git a/ports/arm/platforms/dm36x/dm36x-io.h b/ports/arm/platforms/dm36x/dm36x-io.h
index 567a4eb..3eef8e7 100644
--- a/ports/arm/platforms/dm36x/dm36x-io.h
+++ b/ports/arm/platforms/dm36x/dm36x-io.h
@@ -48,6 +48,7 @@
 #define DM36X_SYSTEM_PINMUX2    0x08
 #define DM36X_SYSTEM_PINMUX3    0x0C
 #define DM36X_SYSTEM_PINMUX4    0x10
+#define DM36X_SYSTEM_PERICLKCTL 0x48
 /* PINMUX0 register bitfields */
 #define DM36X_PINMUX0_MMCSD0     24
 #define DM36X_PINMUX0_GIO49      23