diff --git a/cspot/src/PlainConnection.cpp b/cspot/src/PlainConnection.cpp
index 1bff6cf..b4ee6ff 100644
--- a/cspot/src/PlainConnection.cpp
+++ b/cspot/src/PlainConnection.cpp
@@ -150,6 +150,10 @@ void PlainConnection::readBlock(const uint8_t* dst, size_t size) {
         case EINTR:
           break;
         default:
+          // diagnostic (project patch): n == 0 means the peer closed (FIN); n < 0 with errno
+          // e.g. ECONNRESET (RST). Note errno is not updated when n == 0.
+          CSPOT_LOG(error, "recv returned %d, errno %d, %u of %u bytes, retry %d", (int)n,
+                    getErrno(), idx, (unsigned)size, retries);
           if (retries++ > 4)
             throw std::runtime_error("Error in read");
           goto READ;