diff --git a/lib/types.js b/lib/types.js
index 63726fc3..7e96c26a 100644
--- a/lib/types.js
+++ b/lib/types.js
@@ -361,7 +361,7 @@ function toPrimitive_TIMESTAMP_MILLIS(value) {
 }
 
 function fromPrimitive_TIMESTAMP_MILLIS(value) {
-  return new Date(+value);
+  return new Date(parseInt(value));
 }
 
 function toPrimitive_TIMESTAMP_MICROS(value) {
@@ -382,7 +382,13 @@ function toPrimitive_TIMESTAMP_MICROS(value) {
 }
 
 function fromPrimitive_TIMESTAMP_MICROS(value) {
-  return new Date(parseInt(value / 1000n));
+  if (value === undefined) {
+    return new Date(Nan);
+  } else if (typeof value === 'bigint') {
+    return new Date(parseInt(value / 1000n));
+  } else {
+    return new Date(value / 1000);
+  }
 }
 
 function toPrimitive_INTERVAL(value) {