diff --git a/fdostream.cpp b/fdostream.cpp
index 3c2ed1b..d087312 100644
--- a/fdostream.cpp
+++ b/fdostream.cpp
@@ -16,13 +16,22 @@
 
 std::streambuf::int_type sc::io::fdoutbuf::overflow(std::streambuf::int_type c) {
     if (c != EOF) {
-        if (::write(_fd, &c, 1) != 1) {
+        int res;
+        if ((res = ::write(_fd, &c, 1)) != 1) {
             return EOF;
         }
+        else {
+            std::cerr << "write result = " << res << ", errno = " << errno << '\n';
+        }
     }
     return c;
 }
 
 std::streamsize sc::io::fdoutbuf::xsputn(const char* s, std::streamsize num) {
-    return ::write(_fd, s, num);
+    int res = ::write(_fd, s, num);
+    if (res != num) {
+        std::cerr << "write result = " << res << ", errno = " << errno << '\n';
+        return EOF;
+    }
+    return res;
 }