diff --git a/appl/telnet/acconfig.h b/appl/telnet/acconfig.h
index 6f2ce69b1..d8a0c4af6 100644
--- a/appl/telnet/acconfig.h
+++ b/appl/telnet/acconfig.h
@@ -107,7 +107,7 @@
 #define FILIO_H 1
 #define STREAMS 1
 
-#ifdef __svr4__
+#if defined(__svr4__) || defined(__SVR4)
 #define SOLARIS
 #endif