diff --git a/editcap.c b/editcap.c
index f7feb515826..f7753591942 100644
--- a/editcap.c
+++ b/editcap.c
@@ -1020,18 +1020,43 @@ editcap_dump_open(const char *filename, const wtap_dump_params *params,
                                               WTAP_BLOCK_IF_ID_AND_INFO) != BLOCK_NOT_SUPPORTED) {
         for (guint i = 0; i < idbs_seen->len; i++) {
             wtap_block_t if_data = g_array_index(idbs_seen, wtap_block_t, i);
+            wtap_block_t if_data_copy;
 
             /*
-             * Add this IDB to the file to which we're currently writing.
+             * Make a copy of this IDB, so that we can change the
+             * encapsulation type without trashing the original.
              */
-            if (!wtap_dump_add_idb(pdh, if_data, err, err_info)) {
+            if_data_copy = wtap_block_make_copy(if_data);
+
+            /*
+             * If an encapsulation type was specified, override the
+             * encapsulation type of the interface.
+             */
+            if (out_frame_type != -2) {
+                wtapng_if_descr_mandatory_t *if_mand;
+
+                if_mand = (wtapng_if_descr_mandatory_t *)wtap_block_get_mandatory_data(if_data_copy);
+                if_mand->wtap_encap = out_frame_type;
+            }
+
+            /*
+             * Add this possibly-modified IDB to the file to which
+             * we're currently writing.
+             */
+            if (!wtap_dump_add_idb(pdh, if_data_copy, err, err_info)) {
                 int close_err;
                 gchar *close_err_info;
 
                 wtap_dump_close(pdh, &close_err, &close_err_info);
                 g_free(close_err_info);
+                wtap_block_unref(if_data_copy);
                 return NULL;
             }
+
+            /*
+             * Release the copy - wtap_dump_add_idb() makes its own copy.
+             */
+            wtap_block_unref(if_data_copy);
         }
     }
 
@@ -1057,16 +1082,39 @@ process_new_idbs(wtap *wth, wtap_dumper *pdh, GArray *idbs_seen,
             wtap_block_t if_data_copy;
 
             /*
-             * Add this IDB to the file to which we're currently writing.
+             * Make a copy of this IDB, so that we can change the
+             * encapsulation type without trashing the original.
              */
-            if (!wtap_dump_add_idb(pdh, if_data, err, err_info))
+            if_data_copy = wtap_block_make_copy(if_data);
+
+            /*
+             * If an encapsulation type was specified, override the
+             * encapsulation type of the interface.
+             */
+            if (out_frame_type != -2) {
+                wtapng_if_descr_mandatory_t *if_mand;
+
+                if_mand = (wtapng_if_descr_mandatory_t *)wtap_block_get_mandatory_data(if_data_copy);
+                if_mand->wtap_encap = out_frame_type;
+            }
+
+            /*
+             * Add this possibly-modified IDB to the file to which
+             * we're currently writing.
+             */
+            if (!wtap_dump_add_idb(pdh, if_data_copy, err, err_info))
                 return FALSE;
 
             /*
-             * Also add it to the set of IDBs we've seen, in case we
-             * start writing to another file (which would be of the
-             * same type as the current file, and thus will also require
-             * interface IDs).
+             * Release the copy - wtap_dump_add_idb() makes its own copy.
+             */
+            wtap_block_unref(if_data_copy);
+
+            /*
+             * Also add an unmodified copy to the set of IDBs we've seen,
+             * in case we start writing to another file (which would be
+             * of the same type as the current file, and thus will also
+             * require interface IDs).
              */
             if_data_copy = wtap_block_make_copy(if_data);
             g_array_append_val(idbs_seen, if_data_copy);