diff --git a/Include/allobjects.h b/Include/allobjects.h
index 03b6363a110..641ffeaeab4 100644
--- a/Include/allobjects.h
+++ b/Include/allobjects.h
@@ -41,6 +41,12 @@ OF OR IN CONNECTION WITH THE USE OR PERFORMANCE OF THIS SOFTWARE.
 #define UsingSharedLibs
 #endif
 
+#ifdef WITH_THREAD
+/* This turns errno in a thread-safe function on Solaris.
+   Wonder what it will break though :-( */
+#define _REENTRANT
+#endif
+
 #include <stdio.h>
 #include <string.h>
 #include <errno.h>