diff --git a/host/lib/include/subprocess.h b/host/lib/include/subprocess.h
index eaf7550..b24b987 100644
--- a/host/lib/include/subprocess.h
+++ b/host/lib/include/subprocess.h
@@ -85,22 +85,22 @@
 /**
  * A convenience subprocess target which uses TARGET_NULL.
  */
-struct subprocess_target subprocess_null;
+extern struct subprocess_target subprocess_null;
 
 /**
  * A convenience subprocess target which uses TARGET_FD to STDIN_FILENO.
  */
-struct subprocess_target subprocess_stdin;
+extern struct subprocess_target subprocess_stdin;
 
 /**
  * A convenience subprocess target which uses TARGET_FD to STDOUT_FILENO.
  */
-struct subprocess_target subprocess_stdout;
+extern struct subprocess_target subprocess_stdout;
 
 /**
  * A convenience subprocess target which uses TARGET_FD to STDERR_FILENO.
  */
-struct subprocess_target subprocess_stderr;
+extern struct subprocess_target subprocess_stderr;
 
 /**
  * Call a process and run until completion.