diff --git a/src/memory/map.cpp b/src/memory/map.cpp
index 0c34eeca..179ba88e 100644
--- a/src/memory/map.cpp
+++ b/src/memory/map.cpp
@@ -279,7 +279,7 @@ memory_ptr map::set(size_t offset, size_t size, uint8_t backfill) NOEXCEPT
 
             // Fill new capacity as offset may not be at end due to expansion.
             BC_PUSH_WARNING(NO_POINTER_ARITHMETIC)
-            std::fill_n(memory_map_ + old_capacity, new_capacity - old_capacity,
+            std::fill_n(memory_map_ + logical_, new_capacity - logical_,
                 backfill);
             BC_POP_WARNING()
         }
diff --git a/test/memory/map.cpp b/test/memory/map.cpp
index 8ca9e541..e1d2738f 100644
--- a/test/memory/map.cpp
+++ b/test/memory/map.cpp
@@ -549,11 +549,10 @@ BOOST_AUTO_TEST_CASE(map__set__loaded__expected_fill)
     BOOST_REQUIRE_EQUAL(data[ 5], 'a');     // offset + 0
     BOOST_REQUIRE_EQUAL(data[ 6], 'b');     // offset + 1
     BOOST_REQUIRE_EQUAL(data[ 7], 'c');     // offset + 2
-    BOOST_REQUIRE_EQUAL(data[ 8], fill1);   // expansion
-    BOOST_REQUIRE_EQUAL(data[ 9], fill1);   // expansion
-    BOOST_REQUIRE_EQUAL(data[10], fill1);   // expansion
-    BOOST_REQUIRE_EQUAL(data[11], fill1);   // sub1(offset + size + to_half(offset + size))
-
+    BOOST_REQUIRE_EQUAL(data[ 8], fill2);   // expansion, macos trims on remap here.
+    BOOST_REQUIRE_EQUAL(data[ 9], fill2);   // expansion, so it goes to zero if not refilled.
+    BOOST_REQUIRE_EQUAL(data[10], fill2);   // expansion
+    BOOST_REQUIRE_EQUAL(data[11], fill2);   // sub1(offset + size + to_half(offset + size))
     BOOST_REQUIRE_EQUAL(data[12], fill2);   // cannot assume mmap default fill
     BOOST_REQUIRE_EQUAL(data[13], fill2);   // cannot assume mmap default fill
     BOOST_REQUIRE_EQUAL(data[14], fill2);   // cannot assume mmap default fill