diff --git a/src/ndhc.h b/src/ndhc.h
index 467a102..76a4e6c 100644
--- a/src/ndhc.h
+++ b/src/ndhc.h
@@ -36,7 +36,7 @@
 
 struct client_state_t {
     struct nk_random_state_u32 rnd32_state;
-    unsigned long long leaseStartTime, renewTime, rebindTime;
+    long long leaseStartTime, renewTime, rebindTime;
     long long dhcp_wake_ts;
     int ifsPrevState;
     int ifDeconfig; // Set if the interface has already been deconfigured.
diff --git a/src/sys.h b/src/sys.h
index 598bc8a..b3bc685 100644
--- a/src/sys.h
+++ b/src/sys.h
@@ -31,11 +31,11 @@
 #include <time.h>
 #include "ndhc-defines.h"
 
-static inline unsigned long long curms()
+static inline long long curms()
 {
     struct timespec ts;
     clock_gettime(CLOCK_MONOTONIC, &ts);
-    return ts.tv_sec * 1000ULL + ts.tv_nsec / 1000000ULL;
+    return ts.tv_sec * 1000LL + ts.tv_nsec / 1000000LL;
 }
 
 static inline size_t min_size_t(size_t a, size_t b)