diff --git a/src/native/libs/System.Native/pal_memory.c b/src/native/libs/System.Native/pal_memory.c
index c5398b441989ae..e4034f15298e30 100644
--- a/src/native/libs/System.Native/pal_memory.c
+++ b/src/native/libs/System.Native/pal_memory.c
@@ -17,7 +17,7 @@
 #elif HAVE_MALLOC_USABLE_SIZE_NP
     #include <malloc_np.h>
     #define MALLOC_SIZE(s) malloc_usable_size(s)
-#elif defined(TARGET_SUNOS)
+#elif defined(TARGET_OPENBSD) || defined(TARGET_SUNOS)
     #define MALLOC_SIZE(s) (*((size_t*)(s)-1))
 #else
     #error "Platform doesn't support malloc_usable_size or malloc_size"