diff --git a/src/builtin.c b/src/builtin.c
index ac36a7d6..5120888d 100644
--- a/src/builtin.c
+++ b/src/builtin.c
@@ -1757,7 +1757,7 @@ static jv f_gmtime(jq_state *jq, jv a) {
   struct tm tm, *tmp;
   memset(&tm, 0, sizeof(tm));
   double fsecs = jv_number_value(a);
-  time_t secs = fsecs;
+  time_t secs = floor(fsecs);
   jv_free(a);
   tmp = gmtime_r(&secs, &tm);
   if (tmp == NULL)
@@ -1771,7 +1771,7 @@ static jv f_gmtime(jq_state *jq, jv a) {
   struct tm tm, *tmp;
   memset(&tm, 0, sizeof(tm));
   double fsecs = jv_number_value(a);
-  time_t secs = fsecs;
+  time_t secs = floor(fsecs);
   jv_free(a);
   tmp = gmtime(&secs);
   if (tmp == NULL)
@@ -1792,7 +1792,7 @@ static jv f_localtime(jq_state *jq, jv a) {
   struct tm tm, *tmp;
   memset(&tm, 0, sizeof(tm));
   double fsecs = jv_number_value(a);
-  time_t secs = fsecs;
+  time_t secs = floor(fsecs);
   jv_free(a);
   tmp = localtime_r(&secs, &tm);
   if (tmp == NULL)
@@ -1806,7 +1806,7 @@ static jv f_localtime(jq_state *jq, jv a) {
   struct tm tm, *tmp;
   memset(&tm, 0, sizeof(tm));
   double fsecs = jv_number_value(a);
-  time_t secs = fsecs;
+  time_t secs = floor(fsecs);
   jv_free(a);
   tmp = localtime(&secs);
   if (tmp == NULL)
diff --git a/tests/optional.test b/tests/optional.test
index 77354cce..65e488ba 100644
--- a/tests/optional.test
+++ b/tests/optional.test
@@ -10,3 +10,11 @@ strftime("%A, %B %e, %Y")
 1435677542.822351
 "Tuesday, June 30, 2015"
 
+# Timestamps before the epoch are not supported on mingw/WIN32
+gmtime
+-1.25
+[1969,11,31,23,59,58.75,3,364]
+
+map(gmtime) | . == sort
+[-1.5,-1,-0.5,0,0.5,1,1.5]
+true