diff --git a/src/runtime/mbitmap.go b/src/runtime/mbitmap.go
index afaec55569..38d994eb5a 100644
--- a/src/runtime/mbitmap.go
+++ b/src/runtime/mbitmap.go
@@ -257,7 +257,7 @@ func (s *mspan) objIndex(p uintptr) uintptr {
 		return 0
 	}
 	if s.baseMask != 0 {
-		// s.baseMask is 0, elemsize is a power of two, so shift by s.divShift
+		// s.baseMask is non-0, elemsize is a power of two, so shift by s.divShift
 		return byteOffset >> s.divShift
 	}
 	return uintptr(((uint64(byteOffset) >> s.divShift) * uint64(s.divMul)) >> s.divShift2)