diff --git a/src/gmt.h b/src/gmt.h
index d4c9c20..ea6ddc5 100644
--- a/src/gmt.h
+++ b/src/gmt.h
@@ -34,9 +34,11 @@ extern "C" {
 
 /*  GMT is POSIX.1 COMPLIANT  */
 
+/*
 #ifndef _POSIX_SOURCE
 #define _POSIX_SOURCE 1
 #endif
+*/
 
 /* Declaration modifiers for DLL support (MSC et al) */