diff --git a/vm/os-freebsd.h b/vm/os-freebsd.h
index c535e2d71f..5cedbc82b7 100644
--- a/vm/os-freebsd.h
+++ b/vm/os-freebsd.h
@@ -10,3 +10,7 @@ extern int getosreldate(void);
 
 #define UNKNOWN_TYPE_P(file) ((file)->d_type == DT_UNKNOWN)
 #define DIRECTORY_P(file) ((file)->d_type == DT_DIR)
+
+#ifndef environ
+	extern char **environ;
+#endif
diff --git a/vm/os-linux.h b/vm/os-linux.h
index af47f7bcea..21e34c98f8 100644
--- a/vm/os-linux.h
+++ b/vm/os-linux.h
@@ -1,2 +1,6 @@
 #define UNKNOWN_TYPE_P(file) ((file)->d_type == DT_UNKNOWN)
 #define DIRECTORY_P(file) ((file)->d_type == DT_DIR)
+
+#ifndef environ
+	extern char **environ;
+#endif