diff --git a/cmake/cmake.h.in b/cmake/cmake.h.in
index ed44b2ca..2041f096 100644
--- a/cmake/cmake.h.in
+++ b/cmake/cmake.h.in
@@ -16,6 +16,7 @@
 #cmakedefine01 HAVE_DWMAPI_H
 
 #cmakedefine NOT_X_WINDOWS
+#cmakedefine OMIT_UTMP
 
 #cmakedefine01 HAVE_ASM_HWCAP_H
 #cmakedefine01 HAVE_SYS_AUXV_H
diff --git a/cmake/platforms/unix.cmake b/cmake/platforms/unix.cmake
index cb47caf9..6a788cb4 100644
--- a/cmake/platforms/unix.cmake
+++ b/cmake/platforms/unix.cmake
@@ -19,6 +19,7 @@ check_include_file(sys/sysctl.h HAVE_SYS_SYSCTL_H)
 check_include_file(sys/types.h HAVE_SYS_TYPES_H)
 check_include_file(glob.h HAVE_GLOB_H)
 check_include_file(utmp.h HAVE_UTMP_H)
+check_include_file(utmpx.h HAVE_UTMPX_H)
 
 check_symbol_exists(futimes "sys/time.h" HAVE_FUTIMES)
 check_symbol_exists(getaddrinfo "sys/types.h;sys/socket.h;netdb.h"
@@ -56,6 +57,12 @@ else()
   set(NO_IPV6 ON)
 endif()
 
+if(HAVE_UTMPX_H)
+  set(OMIT_UTMP OFF)
+else()
+  set(OMIT_UTMP ON)
+endif()
+
 include(cmake/gtk.cmake)
 
 # See if we have X11 available. This requires libX11 itself, and also
diff --git a/unix/pty.c b/unix/pty.c
index 0747b584..625f1bb1 100644
--- a/unix/pty.c
+++ b/unix/pty.c
@@ -227,6 +227,8 @@ static void setup_utmp(char *ttyname, char *location)
     endutxent();
 
 #if HAVE_UPDWTMPX
+    /* Reportedly, AIX 5.1 has <utmpx.h> and pututxline(), but no
+     * updwtmpx(). */
     updwtmpx(WTMPX_FILE, &utmp_entry);
 #endif