Index: lldb/source/Plugins/Process/NetBSD/NativeProcessNetBSD.cpp
===================================================================
--- lldb/source/Plugins/Process/NetBSD/NativeProcessNetBSD.cpp
+++ lldb/source/Plugins/Process/NetBSD/NativeProcessNetBSD.cpp
@@ -695,10 +695,10 @@
     io.piod_addr = dst + bytes_read;
 
     Status error = NativeProcessNetBSD::PtraceWrapper(PT_IO, GetID(), &io);
-    if (error.Fail())
+    if (error.Fail() || io.piod_len == 0)
       return error;
 
-    bytes_read = io.piod_len;
+    bytes_read += io.piod_len;
     io.piod_len = size - bytes_read;
   } while (bytes_read < size);