diff --git a/lua/wincent/commandt/lib/Makefile b/lua/wincent/commandt/lib/Makefile
index 30630911..ab0b8b3d 100644
--- a/lua/wincent/commandt/lib/Makefile
+++ b/lua/wincent/commandt/lib/Makefile
@@ -3,7 +3,7 @@
 
 SHELL := /bin/bash
 
-CCFLAGS += -std=c17 -Wall -Wextra -Wno-unused-parameter
+CCFLAGS += -std=gnu17 -Wall -Wextra -Wno-unused-parameter
 
 LBITS := $(shell getconf LONG_BIT)
 ifeq ($(LBITS),64)
diff --git a/lua/wincent/commandt/lib/xmap.c b/lua/wincent/commandt/lib/xmap.c
index 9386ebdb..edd9d898 100644
--- a/lua/wincent/commandt/lib/xmap.c
+++ b/lua/wincent/commandt/lib/xmap.c
@@ -5,8 +5,6 @@
 
 #include "xmap.h"
 
-#define _GNU_SOURCE /* for MAP_ANONYMOUS, MAP_NORESERVE */
-
 #include <assert.h> /* for assert() */
 #include <stddef.h> /* for NULL */
 #include <stdlib.h> /* for abort() */
diff --git a/lua/wincent/commandt/lib/xstrdup.c b/lua/wincent/commandt/lib/xstrdup.c
index 727bd514..4afe7ed4 100644
--- a/lua/wincent/commandt/lib/xstrdup.c
+++ b/lua/wincent/commandt/lib/xstrdup.c
@@ -5,8 +5,6 @@
 
 #include "xstrdup.h"
 
-#define _POSIX_C_SOURCE 200809L /* needed in order to see strdup() */
-
 #include <stddef.h> /* for NULL */
 #include <stdlib.h> /* for abort() */
 #include <string.h> /* for strdup() */