diff --git a/windows/winmisc.c b/windows/winmisc.c
index cd8d74ed..ce0a0d1d 100644
--- a/windows/winmisc.c
+++ b/windows/winmisc.c
@@ -222,8 +222,8 @@ const char *win_strerror(int error)
                            MAKELANGID(LANG_NEUTRAL, SUBLANG_DEFAULT),
                            msgtext, lenof(msgtext)-1, NULL)) {
             sprintf(msgtext,
-                    "(unable to format: FormatMessage returned %d)",
-                    GetLastError());
+                    "(unable to format: FormatMessage returned %u)",
+                    (unsigned int)GetLastError());
         } else {
             int len = strlen(msgtext);
             if (len > 0 && msgtext[len-1] == '\n')
diff --git a/windows/winnet.c b/windows/winnet.c
index 680de2a7..c7f68ef9 100644
--- a/windows/winnet.c
+++ b/windows/winnet.c
@@ -478,8 +478,8 @@ const char *winsock_error_string(int error)
                            MAKELANGID(LANG_NEUTRAL, SUBLANG_DEFAULT),
                            es->text + bufused, bufsize - bufused, NULL)) {
             sprintf(es->text + bufused,
-                    "Windows error code %d (and FormatMessage returned %d)", 
-                    error, GetLastError());
+                    "Windows error code %d (and FormatMessage returned %u)",
+                    error, (unsigned int)GetLastError());
         } else {
             int len = strlen(es->text);
             if (len > 0 && es->text[len-1] == '\n')