diff --git a/src/hnsw.h b/src/hnsw.h
index 728d5dc..042e0a0 100644
--- a/src/hnsw.h
+++ b/src/hnsw.h
@@ -76,7 +76,7 @@
 #define HnswIsNeighborTuple(tup) ((tup)->type == HNSW_NEIGHBOR_TUPLE_TYPE)
 
 /* 2 * M connections for ground layer */
-#define HnswGetLayerM(m, layer) (layer == 0 ? m * 2 : m)
+#define HnswGetLayerM(m, layer) (layer == 0 ? (m) * 2 : (m))
 
 /* Optimal ML from paper */
 #define HnswGetMl(m) (1 / log(m))