diff --git a/src/lib_ccx/file_functions.c b/src/lib_ccx/file_functions.c
index 2876dfb13..01ed30b63 100644
--- a/src/lib_ccx/file_functions.c
+++ b/src/lib_ccx/file_functions.c
@@ -224,10 +224,13 @@ int init_file_buffer(struct ccx_demuxer *ctx)
 {
 	ctx->filebuffer_start = 0;
 	ctx->filebuffer_pos = 0;
+	// Called for every newly opened file. Whatever the buffer still holds
+	// belongs to the previous file and has been consumed; keeping its byte
+	// count while rewinding the position would replay it as new data.
+	ctx->bytesinbuffer = 0;
 	if (ctx->filebuffer == NULL)
 	{
 		ctx->filebuffer = (unsigned char *)malloc(FILEBUFFERSIZE);
-		ctx->bytesinbuffer = 0;
 	}
 	if (ctx->filebuffer == NULL)
 	{
diff --git a/src/rust/src/demuxer/demux.rs b/src/rust/src/demuxer/demux.rs
index 2b5ded8db..b770890c5 100755
--- a/src/rust/src/demuxer/demux.rs
+++ b/src/rust/src/demuxer/demux.rs
@@ -556,12 +556,16 @@ mod tests {
         let mut ctx = dummy_demuxer();
         let buf = vec![1u8; unsafe { FILEBUFFERSIZE } as usize].into_boxed_slice();
         ctx.filebuffer = Box::into_raw(buf) as *mut u8;
+        let original = ctx.filebuffer;
         ctx.bytesinbuffer = 123;
+        ctx.filebuffer_pos = 123;
         let res = init_file_buffer(&mut ctx);
         assert_eq!(res, 0);
-        assert!(!ctx.filebuffer.is_null());
-        // bytesinbuffer remains unchanged.
-        assert_eq!(ctx.bytesinbuffer, 123);
+        assert_eq!(ctx.filebuffer, original);
+        // The bytes belong to the previously opened file: they must not be
+        // replayed as data of the new one.
+        assert_eq!(ctx.filebuffer_pos, 0);
+        assert_eq!(ctx.bytesinbuffer, 0);
         // Clean up.
         unsafe {
             let _ = Box::from_raw(std::ptr::slice_from_raw_parts_mut(
diff --git a/src/rust/src/file_functions/file.rs b/src/rust/src/file_functions/file.rs
index a0b49b9e4..2de7b5c43 100644
--- a/src/rust/src/file_functions/file.rs
+++ b/src/rust/src/file_functions/file.rs
@@ -40,11 +40,14 @@ pub const FILEBUFFERSIZE: usize = 1024 * 1024 * 16; // 16 Mbytes no less. Minimi
 pub fn init_file_buffer(ctx: &mut CcxDemuxer) -> i32 {
     ctx.filebuffer_start = 0;
     ctx.filebuffer_pos = 0;
+    // Called for every newly opened file. Whatever the buffer still holds
+    // belongs to the previous file and has been consumed; keeping its byte
+    // count while rewinding the position would replay it as new data.
+    ctx.bytesinbuffer = 0;
     if ctx.filebuffer.is_null() {
         let mut buf = vec![0u8; FILEBUFFERSIZE].into_boxed_slice();
         ctx.filebuffer = buf.as_mut_ptr();
         mem::forget(buf);
-        ctx.bytesinbuffer = 0;
     }
     if ctx.filebuffer.is_null() {
         return -1;