diff --git a/backend/common.h b/backend/common.h
index 13228ef6..7b70747c 100644
--- a/backend/common.h
+++ b/backend/common.h
@@ -33,6 +33,10 @@
 #ifndef Z_COMMON_H
 #define Z_COMMON_H
 
+#ifdef __cplusplus
+extern "C" {
+#endif /* __cplusplus */
+
 #ifndef ARRAY_SIZE
 #define ARRAY_SIZE(x) ((int) (sizeof(x) / sizeof((x)[0])))
 #endif
@@ -41,7 +45,9 @@
 #  include <malloc.h>
 #  define z_alloca(nmemb) _alloca(nmemb)
 #else
-#  include <alloca.h>
+#  if !(defined(__FreeBSD__) || defined(__OpenBSD__) || defined(__NetBSD__) || defined(__DragonFly__)) /* BSD */
+#    include <alloca.h>
+#  endif
 #  define z_alloca(nmemb) alloca(nmemb)
 #endif
 
@@ -149,10 +155,6 @@ typedef unsigned __int64 uint64_t;
 #  define set_module_colour(s, y, x, c) do { (s)->encoded_data[(y)][(x)] = (c); } while (0)
 #endif
 
-#ifdef __cplusplus
-extern "C" {
-#endif /* __cplusplus */
-
     INTERNAL int ctoi(const char source);
     INTERNAL char itoc(const int source);
     INTERNAL int to_int(const unsigned char source[], const int length);