diff --git a/devicemodel/hw/platform/rtc.c b/devicemodel/hw/platform/rtc.c
index f8e7dff32..0d424f9c0 100644
--- a/devicemodel/hw/platform/rtc.c
+++ b/devicemodel/hw/platform/rtc.c
@@ -1147,6 +1147,8 @@ int
 vrtc_init(struct vmctx *ctx)
 {
 	struct vrtc *vrtc;
+	size_t lomem, himem;
+	int err;
 	struct rtcdev *rtc;
 	time_t curtime;
 	sigset_t mask;
@@ -1160,6 +1162,28 @@ vrtc_init(struct vmctx *ctx)
 
 	pthread_mutex_init(&vrtc->mtx, NULL);
 
+	/*
+	 * Report guest memory size in nvram cells as required by UEFI.
+	 * Little-endian encoding.
+	 * 0x34/0x35 - 64KB chunks above 16MB, below 4GB
+	 * 0x5b/0x5c/0x5d - 64KB chunks above 4GB
+	 */
+	lomem = vm_get_lowmem_size(ctx);
+	assert(lomem >= 16 * MB);
+	lomem = (lomem - 16 * MB) / (64 * KB);
+	err = vrtc_nvram_write(vrtc, RTC_LMEM_LSB, lomem);
+	assert(err == 0);
+	err = vrtc_nvram_write(vrtc, RTC_LMEM_MSB, lomem >> 8);
+	assert(err == 0);
+
+	himem = vm_get_highmem_size(ctx) / (64 * KB);
+	err = vrtc_nvram_write(vrtc, RTC_HMEM_LSB, himem);
+	assert(err == 0);
+	err = vrtc_nvram_write(vrtc, RTC_HMEM_SB, himem >> 8);
+	assert(err == 0);
+	err = vrtc_nvram_write(vrtc, RTC_HMEM_MSB, himem >> 16);
+	assert(err == 0);
+
 	memset(&rtc_addr, 0, sizeof(struct inout_port));
 	memset(&rtc_data, 0, sizeof(struct inout_port));
 	/*register io port handler for rtc addr*/
diff --git a/devicemodel/include/macros.h b/devicemodel/include/macros.h
index effd83f93..35691e226 100644
--- a/devicemodel/include/macros.h
+++ b/devicemodel/include/macros.h
@@ -13,4 +13,8 @@
 #define _CONCAT_(a, b) a ## b
 #define __CONCAT(a, b) _CONCAT_(a, b)
 
+#define	KB		(1024UL)
+#define	MB		(1024 * 1024UL)
+#define	GB		(1024 * 1024 * 1024UL)
+
 #endif
diff --git a/devicemodel/include/rtc.h b/devicemodel/include/rtc.h
index d6b8ff777..08bfdbb5e 100644
--- a/devicemodel/include/rtc.h
+++ b/devicemodel/include/rtc.h
@@ -33,6 +33,12 @@
 
 #define IO_RTC	0x070	/* RTC */
 
+#define	RTC_LMEM_LSB	0x34
+#define	RTC_LMEM_MSB	0x35
+#define	RTC_HMEM_LSB	0x5b
+#define	RTC_HMEM_SB	0x5c
+#define	RTC_HMEM_MSB	0x5d
+
 struct vrtc;
 struct vmctx;
 
diff --git a/devicemodel/include/sw_load.h b/devicemodel/include/sw_load.h
index 3c2d9db1b..533cff448 100644
--- a/devicemodel/include/sw_load.h
+++ b/devicemodel/include/sw_load.h
@@ -30,10 +30,6 @@
 
 #define STR_LEN 1024
 
-#define KB      (1024UL)
-#define MB      (1024 * 1024UL)
-#define GB      (1024 * 1024 * 1024UL)
-
 /* E820 memory types */
 #define E820_TYPE_RAM           1   /* EFI 1, 2, 3, 4, 5, 6, 7 */
 /* EFI 0, 11, 12, 13 (everything not used elsewhere) */