diff --git a/src/common/execio.h b/src/common/execio.h
--- a/src/common/execio.h
+++ b/src/common/execio.h
@@ -54,8 +54,8 @@ int execio_open(struct execio **eio, con
    doesn't block,
    returns 0 on success, 1 on failure
 */
-int execio_read(struct execio *eio, void *buf, size_t len, size_t *bytesread);
-int execio_write(struct execio *eio, void *buf, size_t len, size_t *byteswritten);
+int execio_read(struct execio *eio, const void *buf, size_t len, size_t *bytesread);
+int execio_write(struct execio *eio, const void *buf, size_t len, size_t *byteswritten);
 
 /**
   use this function to determine if the using program should keep trying to read/write