diff --git a/tests/tcg/multiarch/system/memory.c b/tests/tcg/multiarch/system/memory.c
index 214f7d4f54b..eaae6929cb3 100644
--- a/tests/tcg/multiarch/system/memory.c
+++ b/tests/tcg/multiarch/system/memory.c
@@ -40,18 +40,21 @@ static void pdot(int count)
 }
 
 /*
- * Helper macros for shift/extract so we can keep our endian handling
- * in one place.
+ * Helper macros for endian handling.
  */
-#define BYTE_SHIFT(b, pos) ((uint64_t)b << (pos * 8))
-#define BYTE_EXTRACT(b, pos) ((b >> (pos * 8)) & 0xff)
+#if __BYTE_ORDER__ == __ORDER_LITTLE_ENDIAN__
+#define BYTE_SHIFT(b, pos) (b << (pos * 8))
+#define BYTE_NEXT(b) ((b)++)
+#elif __BYTE_ORDER__ == __ORDER_BIG_ENDIAN__
+#define BYTE_SHIFT(b, pos) (b << ((sizeof(b) - 1 - (pos)) * 8))
+#define BYTE_NEXT(b) ((b)--)
+#else
+#error Unsupported __BYTE_ORDER__
+#endif
 
 /*
- * Fill the data with ascending value bytes.
- *
- * Currently we only support Little Endian machines so write in
- * ascending address order. When we read higher address bytes should
- * either be zero or higher than the lower bytes.
+ * Fill the data with ascending (for little-endian) or descending (for
+ * big-endian) value bytes.
  */
 
 static void init_test_data_u8(int unused_offset)
@@ -62,14 +65,14 @@ static void init_test_data_u8(int unused_offset)
 
     ml_printf("Filling test area with u8:");
     for (i = 0; i < TEST_SIZE; i++) {
-        *ptr++ = count++;
+        *ptr++ = BYTE_NEXT(count);
         pdot(i);
     }
     ml_printf("done\n");
 }
 
 /*
- * Full the data with alternating positive and negative bytes. This
+ * Fill the data with alternating positive and negative bytes. This
  * should mean for reads larger than a byte all subsequent reads will
  * stay either negative or positive. We never write 0.
  */
@@ -119,7 +122,7 @@ static void init_test_data_u16(int offset)
     reset_start_data(offset);
 
     for (i = 0; i < max; i++) {
-        uint8_t low = count++, high = count++;
+        uint16_t low = BYTE_NEXT(count), high = BYTE_NEXT(count);
         word = BYTE_SHIFT(high, 1) | BYTE_SHIFT(low, 0);
         *ptr++ = word;
         pdot(i);
@@ -139,9 +142,10 @@ static void init_test_data_u32(int offset)
     reset_start_data(offset);
 
     for (i = 0; i < max; i++) {
-        uint8_t b4 = count++, b3 = count++;
-        uint8_t b2 = count++, b1 = count++;
-        word = BYTE_SHIFT(b1, 3) | BYTE_SHIFT(b2, 2) | BYTE_SHIFT(b3, 1) | b4;
+        uint32_t b4 = BYTE_NEXT(count), b3 = BYTE_NEXT(count);
+        uint32_t b2 = BYTE_NEXT(count), b1 = BYTE_NEXT(count);
+        word = BYTE_SHIFT(b1, 3) | BYTE_SHIFT(b2, 2) | BYTE_SHIFT(b3, 1) |
+               BYTE_SHIFT(b4, 0);
         *ptr++ = word;
         pdot(i);
     }
@@ -160,13 +164,13 @@ static void init_test_data_u64(int offset)
     reset_start_data(offset);
 
     for (i = 0; i < max; i++) {
-        uint8_t b8 = count++, b7 = count++;
-        uint8_t b6 = count++, b5 = count++;
-        uint8_t b4 = count++, b3 = count++;
-        uint8_t b2 = count++, b1 = count++;
+        uint64_t b8 = BYTE_NEXT(count), b7 = BYTE_NEXT(count);
+        uint64_t b6 = BYTE_NEXT(count), b5 = BYTE_NEXT(count);
+        uint64_t b4 = BYTE_NEXT(count), b3 = BYTE_NEXT(count);
+        uint64_t b2 = BYTE_NEXT(count), b1 = BYTE_NEXT(count);
         word = BYTE_SHIFT(b1, 7) | BYTE_SHIFT(b2, 6) | BYTE_SHIFT(b3, 5) |
                BYTE_SHIFT(b4, 4) | BYTE_SHIFT(b5, 3) | BYTE_SHIFT(b6, 2) |
-               BYTE_SHIFT(b7, 1) | b8;
+               BYTE_SHIFT(b7, 1) | BYTE_SHIFT(b8, 0);
         *ptr++ = word;
         pdot(i);
     }
@@ -374,12 +378,20 @@ static bool read_test_data_s16(int offset, bool neg_first)
     ml_printf("Reading s16 from %#lx (offset %d, %s):", ptr,
               offset, neg_first ? "neg" : "pos");
 
+    /*
+     * If the first byte is negative, then the last byte is positive.
+     * Therefore the logic below must be flipped for big-endian.
+     */
+#if __BYTE_ORDER__ == __ORDER_BIG_ENDIAN__
+    neg_first = !neg_first;
+#endif
+
     for (i = 0; i < max; i++) {
         int32_t data = *ptr++;
 
         if (neg_first && data < 0) {
             pdot(i);
-        } else if (data > 0) {
+        } else if (!neg_first && data > 0) {
             pdot(i);
         } else {
             ml_printf("Error %d %c 0\n", data, neg_first ? '<' : '>');
@@ -399,12 +411,20 @@ static bool read_test_data_s32(int offset, bool neg_first)
     ml_printf("Reading s32 from %#lx (offset %d, %s):",
               ptr, offset, neg_first ? "neg" : "pos");
 
+    /*
+     * If the first byte is negative, then the last byte is positive.
+     * Therefore the logic below must be flipped for big-endian.
+     */
+#if __BYTE_ORDER__ == __ORDER_BIG_ENDIAN__
+    neg_first = !neg_first;
+#endif
+
     for (i = 0; i < max; i++) {
         int64_t data = *ptr++;
 
         if (neg_first && data < 0) {
             pdot(i);
-        } else if (data > 0) {
+        } else if (!neg_first && data > 0) {
             pdot(i);
         } else {
             ml_printf("Error %d %c 0\n", data, neg_first ? '<' : '>');
