diff --git a/tools/include/xen-tools/common-macros.h b/tools/include/xen-tools/common-macros.h
index 9e27991782..88b4a0e5a6 100644
--- a/tools/include/xen-tools/common-macros.h
+++ b/tools/include/xen-tools/common-macros.h
@@ -69,6 +69,7 @@
 #endif
 
 #define ROUNDUP(x, a) (((x) + (a) - 1) & ~((a) - 1))
+#define ROUNDDOWN(x, a) ((x) & ~((a) - 1))
 
 #define MASK_EXTR(v, m) (((v) & (m)) / ((m) & -(m)))
 #define MASK_INSR(v, m) (((v) * ((m) & -(m))) & (m))
diff --git a/tools/tests/numa/test-numa.c b/tools/tests/numa/test-numa.c
index ed91a2824f..51cc0475c7 100644
--- a/tools/tests/numa/test-numa.c
+++ b/tools/tests/numa/test-numa.c
@@ -154,6 +154,51 @@ int main(int argc, char **argv)
                 { .start = 0x183f8800000ULL, .end = 0x183faabffffULL },
             },
         },
+        /* Found on a pre-production system. */
+        {
+            .affinity = {
+                { .nid = 0, .start = 0x00000000000ULL, .end = 0x000afffffffULL },
+                { .nid = 0, .start = 0x00100000000ULL, .end = 0x0fc4fffffffULL },
+                { .nid = 0, .start = 0x10000000000ULL, .end = 0x103ffffffffULL },
+                { .nid = 1, .start = 0x10400000000ULL, .end = 0x203ffffffffULL },
+            },
+            .ram = {
+                { .start = 0x00000000000ULL, .end = 0x0000009ffffULL },
+                { .start = 0x00000100000ULL, .end = 0x000165bffffULL },
+                { .start = 0x00016600000ULL, .end = 0x0001aa1dfffULL },
+                { .start = 0x0001aa1f000ULL, .end = 0x0001aa53fffULL },
+                { .start = 0x0001aab8000ULL, .end = 0x0001aac6fffULL },
+                { .start = 0x0001aacc000ULL, .end = 0x0006f3fefffULL },
+                { .start = 0x00075dff000ULL, .end = 0x00075dfffffULL },
+                { .start = 0x00076000000ULL, .end = 0x000a7ffffffULL },
+                { .start = 0x00100010000ULL, .end = 0x0fc43ffffffULL },
+                { .start = 0x0fc45000000ULL, .end = 0x0fc47ffffffULL },
+                { .start = 0x0fc49000000ULL, .end = 0x0fc4bffffffULL },
+                { .start = 0x0fc4d000000ULL, .end = 0x0fc4d3bffffULL },
+                { .start = 0x0fc4f000000ULL, .end = 0x0fc4f0fffffULL },
+                { .start = 0x10000000000ULL, .end = 0x203fd7fffffULL },
+            },
+        },
+        /*
+         * Reduction of the issue above: introduce an unaligned middle region
+         * with regards to the hash shift.
+         */
+        {
+            .affinity = {
+                { .nid = 0, .start = 0x00000ULL, .end = 0x00fffULL },
+                /*
+                 * The offset of the region below is not aligned with the hash
+                 * shift: the shift calculation only takes into account the
+                 * start of node address.
+                 */
+                { .nid = 0, .start = 0x01000ULL, .end = 0x04fffULL },
+                { .nid = 1, .start = 0x14000ULL, .end = 0x14fffULL },
+            },
+            .ram = {
+                { .start = 0x00000ULL, .end = 0x04fffULL },
+                { .start = 0x14000ULL, .end = 0x14fffULL },
+            },
+        },
     };
     int ret_code = EXIT_SUCCESS;
 
diff --git a/xen/common/numa.c b/xen/common/numa.c
index 8544a15982..92f8f1cedc 100644
--- a/xen/common/numa.c
+++ b/xen/common/numa.c
@@ -405,6 +405,12 @@ static int __init populate_memnodemap(const struct node *nodes,
         if ( (epdx >> shift) >= memnodemapsize )
             return 0;
 
+        /*
+         * Round down start address: if start is not aligned to the memnodemap
+         * chunk size the tail remainder might not be added.  Overlaps created
+         * by rounding will fall into the same NUMA region.
+         */
+        spdx = ROUNDDOWN(spdx, 1UL << shift);
         do {
             if ( memnodemap[spdx >> shift] != NUMA_NO_NODE &&
                  (!nodeids || memnodemap[spdx >> shift] != nodeids[i]) )