diff --git a/src/common/buffer.cc b/src/common/buffer.cc
index 548abc458fd..44b7482213b 100644
--- a/src/common/buffer.cc
+++ b/src/common/buffer.cc
@@ -1519,16 +1519,18 @@ static ceph::spinlock debug_lock;
    */
   char *buffer::list::c_str()
   {
-    if (_buffers.empty())
-      return 0;                         // no buffers
-
-    auto iter = std::cbegin(_buffers);
-    ++iter;
-
-    if (iter != std::cend(_buffers)) {
+    switch (get_num_buffers()) {
+    case 0:
+      // no buffers
+      return nullptr;
+    case 1:
+      // good, we're already contiguous.
+      break;
+    default:
       rebuild();
+      break;
     }
-    return _buffers.front().c_str();  // good, we're already contiguous.
+    return _buffers.front().c_str();
   }
 
   string buffer::list::to_str() const {