diff --git a/ext/timeval.cc b/ext/timeval.cc
index 64015e84..9284db62 100644
--- a/ext/timeval.cc
+++ b/ext/timeval.cc
@@ -32,6 +32,7 @@
  */
 
 #include <limits>
+#include <cstdint>
 
 #include "grpc/grpc.h"
 #include "grpc/support/time.h"
@@ -46,7 +47,7 @@ gpr_timespec MillisecondsToTimespec(double millis) {
   } else if (millis == -std::numeric_limits<double>::infinity()) {
     return gpr_inf_past(GPR_CLOCK_REALTIME);
   } else {
-    return gpr_time_from_micros(static_cast<long>(millis * 1000),
+    return gpr_time_from_micros(static_cast<int64_t>(millis * 1000),
                                 GPR_CLOCK_REALTIME);
   }
 }