diff --git a/CHANGES b/CHANGES
index a777a0500e..d2a0f65f6e 100644
--- a/CHANGES
+++ b/CHANGES
@@ -1,3 +1,6 @@
+5722.	[bug]		Preserve the contents of TCPDNS and TLSDNS receive
+			buffer when growing the buffer size. [GL #2917]
+
 5721.	[func]		New isc_mem_reget() realloc-like function was
 			introduced into the libisc API, and zero-sized
 			allocations now return non-NULL pointers. [GL !5440]
diff --git a/doc/notes/notes-current.rst b/doc/notes/notes-current.rst
index cfa98cedde..46c66f04ad 100644
--- a/doc/notes/notes-current.rst
+++ b/doc/notes/notes-current.rst
@@ -62,3 +62,6 @@ Bug Fixes
 - When new IP addresses were added to the system during ``named``
   startup, ``named`` failed to listen on TCP for the newly added
   interfaces. :gl:`#2852`
+
+- Under specific circumstances, zone transfers over TCP and TLS could be
+  interrupted prematurely. This has been fixed. :gl:`#2917`
diff --git a/lib/isc/netmgr/netmgr.c b/lib/isc/netmgr/netmgr.c
index 5b1ff7cdb8..a74047d763 100644
--- a/lib/isc/netmgr/netmgr.c
+++ b/lib/isc/netmgr/netmgr.c
@@ -1894,8 +1894,8 @@ isc__nm_alloc_dnsbuf(isc_nmsocket_t *sock, size_t len) {
 		sock->buf_size = alloc_len;
 	} else {
 		/* We have the buffer but it's too small */
-		isc_mem_put(sock->mgr->mctx, sock->buf, sock->buf_size);
-		sock->buf = isc_mem_get(sock->mgr->mctx, NM_BIG_BUF);
+		sock->buf = isc_mem_reget(sock->mgr->mctx, sock->buf,
+					  sock->buf_size, NM_BIG_BUF);
 		sock->buf_size = NM_BIG_BUF;
 	}
 }