diff --git a/2019/day01/Makefile b/2019/day01/Makefile
index 7fd5a7c..7100584 100644
--- a/2019/day01/Makefile
+++ b/2019/day01/Makefile
@@ -24,7 +24,7 @@ LDLIB   := -l$(LIB)
 
 export LD_LIBRARY_PATH = $(LIBDIR)
 
-CFLAGS  += -std=gnu99
+CFLAGS  += -std=gnu11
 CFLAGS  += -O2
 CFLAGS  += -g
 # for gprof
diff --git a/2019/day02/Makefile b/2019/day02/Makefile
index 7fd5a7c..7100584 100644
--- a/2019/day02/Makefile
+++ b/2019/day02/Makefile
@@ -24,7 +24,7 @@ LDLIB   := -l$(LIB)
 
 export LD_LIBRARY_PATH = $(LIBDIR)
 
-CFLAGS  += -std=gnu99
+CFLAGS  += -std=gnu11
 CFLAGS  += -O2
 CFLAGS  += -g
 # for gprof
diff --git a/2019/day03/Makefile b/2019/day03/Makefile
index 7fd5a7c..7100584 100644
--- a/2019/day03/Makefile
+++ b/2019/day03/Makefile
@@ -24,7 +24,7 @@ LDLIB   := -l$(LIB)
 
 export LD_LIBRARY_PATH = $(LIBDIR)
 
-CFLAGS  += -std=gnu99
+CFLAGS  += -std=gnu11
 CFLAGS  += -O2
 CFLAGS  += -g
 # for gprof
diff --git a/2019/day04/Makefile b/2019/day04/Makefile
index 7fd5a7c..7100584 100644
--- a/2019/day04/Makefile
+++ b/2019/day04/Makefile
@@ -24,7 +24,7 @@ LDLIB   := -l$(LIB)
 
 export LD_LIBRARY_PATH = $(LIBDIR)
 
-CFLAGS  += -std=gnu99
+CFLAGS  += -std=gnu11
 CFLAGS  += -O2
 CFLAGS  += -g
 # for gprof
diff --git a/2019/day05/Makefile b/2019/day05/Makefile
index 7fd5a7c..7100584 100644
--- a/2019/day05/Makefile
+++ b/2019/day05/Makefile
@@ -24,7 +24,7 @@ LDLIB   := -l$(LIB)
 
 export LD_LIBRARY_PATH = $(LIBDIR)
 
-CFLAGS  += -std=gnu99
+CFLAGS  += -std=gnu11
 CFLAGS  += -O2
 CFLAGS  += -g
 # for gprof
diff --git a/2019/day06/Makefile b/2019/day06/Makefile
index 7fd5a7c..7100584 100644
--- a/2019/day06/Makefile
+++ b/2019/day06/Makefile
@@ -24,7 +24,7 @@ LDLIB   := -l$(LIB)
 
 export LD_LIBRARY_PATH = $(LIBDIR)
 
-CFLAGS  += -std=gnu99
+CFLAGS  += -std=gnu11
 CFLAGS  += -O2
 CFLAGS  += -g
 # for gprof