diff --git a/src/hal/ambarella_test.c b/src/hal/ambarella_test.c
index d8c6518..63ca1c7 100644
--- a/src/hal/ambarella_test.c
+++ b/src/hal/ambarella_test.c
@@ -8,6 +8,7 @@
 #include <unistd.h>
 
 #include "hal/ambarella.h"
+#include "hal/common.h"
 
 int chip_generation;
 char chip_name[128];
@@ -93,6 +94,13 @@ int main() {
     unlink(path);
     CHECK(!ambarella_iavmem_from_dt(path, &start, &size));
 
+    /* ram.c rounds the total up to a power of two; on this board the total
+     * already is one and must stay 512M, not become 1024M. */
+    CHECK(rounded_num((0x07800000u + 0x18800000u) / 1024 / 1024) == 512);
+    CHECK(rounded_num(112) == 128); /* a MemTotal of 114940 kB */
+    CHECK(rounded_num(513) == 1024);
+    CHECK(rounded_num(1) == 1);
+
     if (failures)
         return EXIT_FAILURE;
     puts("ambarella_test: all cases passed");
diff --git a/src/hal/common.c b/src/hal/common.c
index b449d94..20fa94e 100644
--- a/src/hal/common.c
+++ b/src/hal/common.c
@@ -268,6 +268,9 @@ unsigned long kernel_mem() {
 }
 
 uint32_t rounded_num(uint32_t n) {
+    if (n && !(n & (n - 1)))
+        return n;
+
     int i;
     for (i = 0; n; i++) {
         n /= 2;