diff --git a/src/net.c b/src/net.c
index a8c327908..8f28c03ad 100644
--- a/src/net.c
+++ b/src/net.c
@@ -459,6 +459,17 @@ Nrecv(int fd, char *buf, size_t count, int prot, int sock_opt)
             break;
 
 	if (sock_opt & MSG_TRUNC) {
+            /*
+             * On a datagram socket MSG_TRUNC returns the full datagram length
+             * even though only `count` bytes were copied.  That length is the
+             * value the caller must account (fastpath fix: upstream returned
+             * `count`, so UDP --skip-rx-copy under-reported throughput ~100x).
+             */
+            if (prot == SOCK_DGRAM) { /* Pudp; iperf_api.h is not included here */
+                if (r < count)
+                    return NET_HARDERROR; /* at least the UDP message header must be present */
+                return r;
+            }
             size_t bytes_copied = (r > nleft)? nleft: r;
             nleft -= bytes_copied;
             buf += bytes_copied;
@@ -538,6 +549,17 @@ Nrecv_no_select(int fd, char *buf, size_t count, int prot, int sock_opt)
             break;
 
 	if (sock_opt & MSG_TRUNC) {
+            /*
+             * On a datagram socket MSG_TRUNC returns the full datagram length
+             * even though only `count` bytes were copied.  That length is the
+             * value the caller must account (fastpath fix: upstream returned
+             * `count`, so UDP --skip-rx-copy under-reported throughput ~100x).
+             */
+            if (prot == SOCK_DGRAM) { /* Pudp; iperf_api.h is not included here */
+                if (r < count)
+                    return NET_HARDERROR; /* at least the UDP message header must be present */
+                return r;
+            }
             size_t bytes_copied = (r > nleft)? nleft: r;
             nleft -= bytes_copied;
             buf += bytes_copied;