diff --git a/include/PR/os_libc.h b/include/PR/os_libc.h
index 13ec2124..4c2fc3e1 100644
--- a/include/PR/os_libc.h
+++ b/include/PR/os_libc.h
@@ -6,8 +6,8 @@
 // Old deprecated functions from strings.h, replaced by memcpy/memset.
 #ifdef NO_BZERO
 #include <string.h>
-#define bzero(buf, size) memset(buf, 0, size)
-#define bcopy(src, dst, size) memcpy(dst, src, size)
+#define bzero(buf, size) memset((buf), 0, (size))
+#define bcopy(src, dst, size) memcpy((dst), (src), (size))
 #else
 extern void bcopy(const void *, void *, size_t);
 extern void bzero(void *, size_t);