diff --git a/man7/ftm.7 b/man7/ftm.7
index fb24d1ae9..2d0a65de5 100644
--- a/man7/ftm.7
+++ b/man7/ftm.7
@@ -60,7 +60,7 @@ definitions for POSIX.1c (threads).
 Defining with the value 200112 exposes definitions corresponding 
 to the POSIX.1-2001 base specification (excluding the XSI extension).
 .TP 
-.B _POSIX_C_SOURCE
+.B _POSIX_SOURCE
 Defining this obsolete macro with any value is equivalent to defining
 .B _POSIX_C_SOURCE
 with the value 1.