diff --git a/tests/test_datetime.rs b/tests/test_datetime.rs
old mode 100644
new mode 100755
index 52b98c0a..5493d751
--- a/tests/test_datetime.rs
+++ b/tests/test_datetime.rs
@@ -54,10 +54,21 @@ macro_rules! assert_check_only {
     };
 }
 
+// Because of the relase pool unsoundness reported in https://github.com/PyO3/pyo3/issues/756,
+// we need to stop other threads before calling `py.import()`.
+// TODO(kngwyu): Remove this macro
+macro_rules! lock {
+    () => {
+        let _mutex = std::sync::Mutex::new(());
+        let _lock = _mutex.lock().unwrap();
+    };
+}
+
 #[test]
 fn test_date_check() {
     let gil = Python::acquire_gil();
     let py = gil.python();
+    lock!();
     let (obj, sub_obj, sub_sub_obj) = _get_subclasses(&py, "date", "2018, 1, 1").unwrap();
 
     assert_check_exact!(PyDate_Check, obj);
@@ -69,6 +80,7 @@ fn test_date_check() {
 fn test_time_check() {
     let gil = Python::acquire_gil();
     let py = gil.python();
+    lock!();
     let (obj, sub_obj, sub_sub_obj) = _get_subclasses(&py, "time", "12, 30, 15").unwrap();
 
     assert_check_exact!(PyTime_Check, obj);
@@ -80,6 +92,7 @@ fn test_time_check() {
 fn test_datetime_check() {
     let gil = Python::acquire_gil();
     let py = gil.python();
+    lock!();
     let (obj, sub_obj, sub_sub_obj) = _get_subclasses(&py, "datetime", "2018, 1, 1, 13, 30, 15")
         .map_err(|e| e.print(py))
         .unwrap();
@@ -94,6 +107,7 @@ fn test_datetime_check() {
 fn test_delta_check() {
     let gil = Python::acquire_gil();
     let py = gil.python();
+    lock!();
     let (obj, sub_obj, sub_sub_obj) = _get_subclasses(&py, "timedelta", "1, -3").unwrap();
 
     assert_check_exact!(PyDelta_Check, obj);
@@ -108,7 +122,7 @@ fn test_datetime_utc() {
 
     let gil = Python::acquire_gil();
     let py = gil.python();
-
+    lock!();
     let datetime = py.import("datetime").map_err(|e| e.print(py)).unwrap();
     let timezone = datetime.get("timezone").unwrap();
     let utc = timezone.getattr("utc").unwrap().to_object(py);