diff --git a/tools/tests/pdx/test-pdx.c b/tools/tests/pdx/test-pdx.c
index d783186577..4de8d43d86 100644
--- a/tools/tests/pdx/test-pdx.c
+++ b/tools/tests/pdx/test-pdx.c
@@ -191,6 +191,20 @@ int main(int argc, char **argv)
             },
             .compress = false,
         },
+        /*
+         * Dell R740, dual socket.  Merging of ranges causes mask differences
+         * in PDX offset mode.  Useful for checking mask calculations.
+         */
+        {
+            .ranges = {
+                { .start = 0x0000000UL, .end = 0x0080000UL },
+                { .start = 0x0100000UL, .end = 0x3070000UL },
+                { .start = 0x3070000UL, .end = 0x3870000UL },
+                { .start = 0x3870000UL, .end = 0x6870000UL },
+                { .start = 0x6870000UL, .end = 0x7070000UL },
+            },
+            .compress = false,
+        },
     };
     int ret_code = EXIT_SUCCESS;
 
diff --git a/xen/common/pdx.c b/xen/common/pdx.c
index 7e070ff962..e7e16e193e 100644
--- a/xen/common/pdx.c
+++ b/xen/common/pdx.c
@@ -391,10 +391,7 @@ bool __init pfn_pdx_compression_setup(paddr_t base)
         if ( !i ||
              ranges[i].base_pfn >=
              (ranges[i - 1].base_pfn + ranges[i - 1].pages) )
-        {
-            mask |= pdx_region_mask(ranges[i].base_pfn, ranges[i].pages);
             continue;
-        }
 
         ranges[i - 1].pages = ranges[i].base_pfn + ranges[i].pages -
                               ranges[i - 1].base_pfn;
@@ -402,19 +399,21 @@ bool __init pfn_pdx_compression_setup(paddr_t base)
         if ( i + 1 < nr_ranges )
             memmove(&ranges[i], &ranges[i + 1],
                     (nr_ranges - (i + 1)) * sizeof(ranges[0]));
-        else /* last range */
-            mask |= pdx_region_mask(ranges[i].base_pfn, ranges[i].pages);
         nr_ranges--;
         i--;
     }
 
     /*
-     * Populate a mask with the non-equal bits of the different ranges, do this
-     * to calculate the maximum PFN shift to use as the lookup table index.
+     * Populate two masks: one with the non-equal bits of the different ranges,
+     * another with the bits that change inside ranges.  Do this to calculate
+     * the maximum PFN shift to use as the lookup table index.
      */
     for ( i = 0; i < nr_ranges; i++ )
+    {
+        mask |= pdx_region_mask(ranges[i].base_pfn, ranges[i].pages);
         for ( unsigned int j = i + 1; j < nr_ranges; j++ )
             idx_mask |= ranges[i].base_pfn ^ ranges[j].base_pfn;
+    }
     /* Mask out the bits that change inside of ranges. */
     idx_mask &= ~mask;