diff --git a/os/xdmcp.c b/os/xdmcp.c
index 877b11c153..f5331e1b9f 100644
--- a/os/xdmcp.c
+++ b/os/xdmcp.c
@@ -486,7 +486,7 @@ XdmcpRegisterConnection (
 	    }
 	}
 #endif
-	if (fromAddr && memcmp(regAddr, fromAddr, regAddrlen) != 0) {
+	if (!fromAddr || memcmp(regAddr, fromAddr, regAddrlen) != 0) {
 	    return;
 	}
     }