diff --git a/src/runtime/mheap.go b/src/runtime/mheap.go
index 4fcfbeca84..e058dd8489 100644
--- a/src/runtime/mheap.go
+++ b/src/runtime/mheap.go
@@ -1839,7 +1839,7 @@ const (
 type special struct {
 	_      sys.NotInHeap
 	next   *special // linked list in span
-	offset uint16   // span offset of object
+	offset uintptr  // span offset of object
 	kind   byte     // kind of special
 }
 
@@ -1886,7 +1886,7 @@ func addspecial(p unsafe.Pointer, s *special, force bool) bool {
 	iter, exists := span.specialFindSplicePoint(offset, kind)
 	if !exists || force {
 		// Splice in record, fill in offset.
-		s.offset = uint16(offset)
+		s.offset = offset
 		s.next = *iter
 		*iter = s
 		spanHasSpecials(span)
diff --git a/src/runtime/pinner.go b/src/runtime/pinner.go
index 7a9c381580..543bfdb7a4 100644
--- a/src/runtime/pinner.go
+++ b/src/runtime/pinner.go
@@ -331,7 +331,7 @@ func (span *mspan) incPinCounter(offset uintptr) {
 		rec = (*specialPinCounter)(mheap_.specialPinCounterAlloc.alloc())
 		unlock(&mheap_.speciallock)
 		// splice in record, fill in offset.
-		rec.special.offset = uint16(offset)
+		rec.special.offset = offset
 		rec.special.kind = _KindSpecialPinCounter
 		rec.special.next = *ref
 		*ref = (*special)(unsafe.Pointer(rec))
diff --git a/src/weak/pointer_test.go b/src/weak/pointer_test.go
index 213dde8c40..002b4130f0 100644
--- a/src/weak/pointer_test.go
+++ b/src/weak/pointer_test.go
@@ -43,9 +43,11 @@ func TestPointer(t *testing.T) {
 func TestPointerEquality(t *testing.T) {
 	bt := make([]*T, 10)
 	wt := make([]weak.Pointer[T], 10)
+	wo := make([]weak.Pointer[int], 10)
 	for i := range bt {
 		bt[i] = new(T)
 		wt[i] = weak.Make(bt[i])
+		wo[i] = weak.Make(&bt[i].a)
 	}
 	for i := range bt {
 		st := wt[i].Value()
@@ -55,6 +57,9 @@ func TestPointerEquality(t *testing.T) {
 		if wp := weak.Make(st); wp != wt[i] {
 			t.Fatalf("new weak pointer not equal to existing weak pointer: %v vs. %v", wp, wt[i])
 		}
+		if wp := weak.Make(&st.a); wp != wo[i] {
+			t.Fatalf("new weak pointer not equal to existing weak pointer: %v vs. %v", wp, wo[i])
+		}
 		if i == 0 {
 			continue
 		}
@@ -72,6 +77,9 @@ func TestPointerEquality(t *testing.T) {
 		if wp := weak.Make(st); wp != wt[i] {
 			t.Fatalf("new weak pointer not equal to existing weak pointer: %v vs. %v", wp, wt[i])
 		}
+		if wp := weak.Make(&st.a); wp != wo[i] {
+			t.Fatalf("new weak pointer not equal to existing weak pointer: %v vs. %v", wp, wo[i])
+		}
 		if i == 0 {
 			continue
 		}
@@ -210,3 +218,12 @@ func TestIssue69210(t *testing.T) {
 	}
 	wg.Wait()
 }
+
+func TestIssue70739(t *testing.T) {
+	x := make([]*int, 4<<16)
+	wx1 := weak.Make(&x[1<<16])
+	wx2 := weak.Make(&x[1<<16])
+	if wx1 != wx2 {
+		t.Fatal("failed to look up special and made duplicate weak handle; see issue #70739")
+	}
+}