diff --git a/src/plist.c b/src/plist.c
index 4cb6206..862a54c 100644
--- a/src/plist.c
+++ b/src/plist.c
@@ -69,8 +69,8 @@
     int state;
 } thread_once_t;
 
-static thread_once_t init_once = {0, 0};
-static thread_once_t deinit_once = {0, 0};
+static const thread_once_t init_once = {0, 0};
+static const thread_once_t deinit_once = {0, 0};
 
 void thread_once(thread_once_t *once_control, void (*init_routine)(void))
 {
diff --git a/src/time64.c b/src/time64.c
index b62bc86..53932de 100644
--- a/src/time64.c
+++ b/src/time64.c
@@ -59,11 +59,11 @@
     {0, 31, 60, 91, 121, 152, 182, 213, 244, 274, 305, 335},
 };
 
-static char wday_name[7][4] = {
+static const char wday_name[7][4] = {
     "Sun", "Mon", "Tue", "Wed", "Thu", "Fri", "Sat"
 };
 
-static char mon_name[12][4] = {
+static const char mon_name[12][4] = {
     "Jan", "Feb", "Mar", "Apr", "May", "Jun",
     "Jul", "Aug", "Sep", "Oct", "Nov", "Dec"
 };