diff --git a/zetasql/public/functions/date_time_util.cc b/zetasql/public/functions/date_time_util.cc
index b579d10aa..753de449d 100644
--- a/zetasql/public/functions/date_time_util.cc
+++ b/zetasql/public/functions/date_time_util.cc
@@ -2348,6 +2348,17 @@ absl::Status ConvertStringToTimestamp(absl::string_view str,
   return ConvertStringToTimestamp(str, timezone, scale, timestamp);
 }
 
+absl::Status ConvertStringToTimestamp(absl::string_view str,
+                                      absl::string_view default_timezone_string,
+                                      TimestampScale scale,
+                                      bool allow_tz_in_str,
+                                      absl::Time* output) {
+  absl::TimeZone timezone;
+  ZETASQL_RETURN_IF_ERROR(MakeTimeZone(default_timezone_string, &timezone));
+  return ConvertStringToTimestamp(str, timezone, scale, allow_tz_in_str,
+                                  output);
+}
+
 absl::Status ConvertStringToTimestamp(absl::string_view str,
                                       absl::TimeZone default_timezone,
                                       TimestampScale scale,
diff --git a/zetasql/public/functions/date_time_util.h b/zetasql/public/functions/date_time_util.h
index e4b0b34dd..12b7a6152 100644
--- a/zetasql/public/functions/date_time_util.h
+++ b/zetasql/public/functions/date_time_util.h
@@ -412,6 +412,16 @@ absl::Status ConvertStringToTimestamp(absl::string_view str,
                                       TimestampScale scale,
                                       bool allow_tz_in_str, int64_t* timestamp);
 
+// If the time zone is not included in the string, then
+// <default_timezone_string> is applied for the conversion.  Uses the
+// canonical timestamp string format.
+// If the time zone is included in the string and allow_tz_in_str is set to
+// false, an error will be returned.
+absl::Status ConvertStringToTimestamp(absl::string_view str,
+                                      absl::string_view default_timezone_string,
+                                      TimestampScale scale,
+                                      bool allow_tz_in_str, absl::Time* output)
+
 // Populate the <output> with the values from input if the values on all fields
 // are valid, return error otherwise.
 absl::Status ConstructDate(int year, int month, int day, int32_t* output);
diff --git a/zetasql/reference_impl/function.cc b/zetasql/reference_impl/function.cc
index b258838fb..ebed55b09 100644
--- a/zetasql/reference_impl/function.cc
+++ b/zetasql/reference_impl/function.cc
@@ -9231,19 +9231,21 @@ absl::StatusOr<Value> TimestampConversionFunction::Eval(
     }
     return Value::Timestamp(timestamp);
   } else if (!args.empty() && args[0].type()->IsString()) {
-    int64_t timestamp_micros;
+    absl::Time timestamp;
     if (args.size() == 2 && args[1].type()->IsString()) {
       ZETASQL_RETURN_IF_ERROR(functions::ConvertStringToTimestamp(
           args[0].string_value(), args[1].string_value(),
-          functions::kMicroseconds, false, &timestamp_micros));
+          GetTimestampScale(context->GetLanguageOptions()), false, &timestamp));
     } else if (args.size() == 1) {
       ZETASQL_RETURN_IF_ERROR(functions::ConvertStringToTimestamp(
           args[0].string_value(), context->GetDefaultTimeZone(),
-          functions::kMicroseconds, true, &timestamp_micros));
+          GetTimestampScale(context->GetLanguageOptions()), true, &timestamp));
     } else {
       return MakeEvalError() << "Unsupported function: " << debug_name();
     }
-    return Value::TimestampFromUnixMicros(timestamp_micros);
+    const Value result = Value::Timestamp(timestamp);
+    ZETASQL_RETURN_IF_ERROR(ValidateMicrosPrecision(result, context));
+    return result;
   } else if (!args.empty() && args[0].type()->IsDate()) {
     int64_t timestamp_micros;
     if (args.size() == 2 && args[1].type()->IsString()) {