diff --git a/src/nxt_unit.c b/src/nxt_unit.c
index 1fc9acd8d..062b5038e 100644
--- a/src/nxt_unit.c
+++ b/src/nxt_unit.c
@@ -3506,6 +3506,10 @@ nxt_unit_mmap_get(nxt_unit_ctx_t *ctx, nxt_unit_port_t *port,
 
     outgoing_size = lib->outgoing.size;
 
+    if (nxt_slow_path(outgoing_size == 0)) {
+        goto skip;
+    }
+
     mm_end = lib->outgoing.elts + outgoing_size;
 
     for (mm = lib->outgoing.elts; mm < mm_end; mm++) {
@@ -3556,6 +3560,8 @@ nxt_unit_mmap_get(nxt_unit_ctx_t *ctx, nxt_unit_port_t *port,
         hdr->oosm = 1;
     }
 
+skip:
+
     if (outgoing_size >= lib->shm_mmap_limit) {
         /* Cannot allocate more shared memory. */
         pthread_mutex_unlock(&lib->outgoing.mutex);