diff --git a/stream/stream.h b/stream/stream.h
index 2116fdde27..423ba12d91 100644
--- a/stream/stream.h
+++ b/stream/stream.h
@@ -109,7 +109,7 @@ typedef struct stream_info_st {
     // opts is set from ->opts
     int (*open)(struct stream *st);
     // Alternative to open(). Only either open() or open2() can be set.
-    int (*open2)(struct stream *st, struct stream_open_args *args);
+    int (*open2)(struct stream *st, const struct stream_open_args *args);
     const char *const *protocols;
     bool can_write;     // correctly checks for READ/WRITE modes
     bool local_fs;      // supports STREAM_LOCAL_FS_ONLY
diff --git a/stream/stream_concat.c b/stream/stream_concat.c
index 21f04f9d62..d06bd4a782 100644
--- a/stream/stream_concat.c
+++ b/stream/stream_concat.c
@@ -99,7 +99,7 @@ static int combine_origin(int cur, int new)
     return new; // including cur==0
 }
 
-static int open2(struct stream *stream, struct stream_open_args *args)
+static int open2(struct stream *stream, const struct stream_open_args *args)
 {
     struct priv *p = talloc_zero(stream, struct priv);
     stream->priv = p;
diff --git a/stream/stream_file.c b/stream/stream_file.c
index d649ff4bdf..612d4bee38 100644
--- a/stream/stream_file.c
+++ b/stream/stream_file.c
@@ -246,7 +246,7 @@ static bool check_stream_network(int fd)
 }
 #endif
 
-static int open_f(stream_t *stream, struct stream_open_args *args)
+static int open_f(stream_t *stream, const struct stream_open_args *args)
 {
     struct priv *p = talloc_ptrtype(stream, p);
     *p = (struct priv) {
diff --git a/stream/stream_memory.c b/stream/stream_memory.c
index 7383ff4d6f..e4696a73ad 100644
--- a/stream/stream_memory.c
+++ b/stream/stream_memory.c
@@ -44,7 +44,7 @@ static int64_t get_size(stream_t *s)
     return p->data.len;
 }
 
-static int open2(stream_t *stream, struct stream_open_args *args)
+static int open2(stream_t *stream, const struct stream_open_args *args)
 {
     stream->fill_buffer = fill_buffer;
     stream->seek = seek;
diff --git a/stream/stream_slice.c b/stream/stream_slice.c
index 8bf80943eb..c0dbeeb2af 100644
--- a/stream/stream_slice.c
+++ b/stream/stream_slice.c
@@ -136,7 +136,7 @@ static int parse_slice_range(stream_t *stream)
     return STREAM_OK;
 }
 
-static int open2(struct stream *stream, struct stream_open_args *args)
+static int open2(struct stream *stream, const struct stream_open_args *args)
 {
     struct priv *p = talloc_zero(stream, struct priv);
     stream->priv = p;