--- a/mb_ds_util.h	Wed Jun 02 11:09:57 2021 +0100
+++ b/mb_ds_util.h	Sun Jun 06 22:40:06 2021 +0100
@@ -97,6 +97,7 @@
         int data_start;     /* offset within *data were valid data starts */
         int data_end;       /* offset within *data were valid data ends   */
         int max_data_start; /* optimization parameter! When should it be normalised? */
+        int marked_for_purge; /* Number of bytes to be deleted in next call to lb_data_purge() */
         } lb_buf_t;
 
 /* NOTE: lb = Linear Buffer */
@@ -111,6 +112,7 @@
   buf->data_size  = size;
   buf->data_start = 0;
   buf->data_end   = 0;
+  buf->marked_for_purge = 0;
   buf->max_data_start = max_data_start;
   buf->data = (u8 *)malloc(size);
   return buf->data;
@@ -143,8 +145,13 @@
     buf->data_end = buf->data_size - 1;
 }
 
+static inline void lb_data_mark_for_purge(lb_buf_t *buf, int count) {
+  buf->marked_for_purge += count;
+}
+
 static inline u8 *lb_data_purge(lb_buf_t *buf, int count) {
-  buf->data_start += count;
+  buf->data_start += count + buf->marked_for_purge;
+  buf->marked_for_purge = 0;
   if (buf->data_start > buf->data_end)
     buf->data_start = buf->data_end;
 
@@ -156,6 +163,7 @@
 
 static inline void lb_data_purge_all(lb_buf_t *buf) {
   buf->data_start = buf->data_end = 0;
+  buf->marked_for_purge = 0;
 }
 
 static inline u8 *lb_free(lb_buf_t *buf) {

--- a/mb_rtu.c	Wed Jun 02 11:09:57 2021 +0100
+++ b/mb_rtu.c	Sun Jun 06 22:40:06 2021 +0100
@@ -1422,8 +1422,11 @@
 #endif
     /* set the data pointer */
   *recv_data_ptr = lb_data(&(buf->data_buf));
-    /* remove the frame bytes off the buffer */
-  lb_data_purge(&(buf->data_buf), frame_length);
+    /* Mark the frame bytes to be deleted off the buffer by the next call to lb_data_purge() */
+	/* Notice that we cannot delete the frame bytes right away, as they will still be accessed by whoever
+	 * called read_frame(). We can only delete this data on the next call to read_frame() 
+	 */
+  lb_data_mark_for_purge(&(buf->data_buf), frame_length);
     /* reset the search_history flag */
   buf->frame_search_history = 0;
     /* if the buffer becomes empty, then reset boundary flag */
@@ -1532,6 +1535,16 @@
   *recv_data_ptr = NULL;
 
   /*===================================*
+   * Delete any previously received data that has already been returned as a valid frame in *
+   *===================================*/  
+   /* Delete any previously received data that has already been returned as a valid frame in 
+    * the previous invocation of read_frame().
+	* Notice that the data that will be deleted hass ben marked for deletion by calling
+	* lb_data_mark_for_purge() in return_frame()
+	*/
+  lb_data_purge(&(recv_buf->data_buf), 0);
+
+  /*===================================*
    * Check for frame in left over data *
    *===================================*/
   /* If we have any data left over from previous call to read_frame()