diff --git a/crates/open_jtalk/src/jpcommon.rs b/crates/open_jtalk/src/jpcommon.rs
index d31ad19..7f97c50 100644
--- a/crates/open_jtalk/src/jpcommon.rs
+++ b/crates/open_jtalk/src/jpcommon.rs
@@ -32,6 +32,9 @@ unsafe impl resources::Resource for JpCommon {
     }
 }
 
+// SAFETY: `Send`と対立する性質はないはず。
+unsafe impl Send for JpCommon {}
+
 impl<'a> Iterator for JpCommonLabelFeatureIter<'a> {
     type Item = &'a str;
     fn next(&mut self) -> Option<Self::Item> {
diff --git a/crates/open_jtalk/src/mecab/mod.rs b/crates/open_jtalk/src/mecab/mod.rs
index 42fb31c..5f8b81c 100644
--- a/crates/open_jtalk/src/mecab/mod.rs
+++ b/crates/open_jtalk/src/mecab/mod.rs
@@ -39,6 +39,9 @@ unsafe impl resources::Resource for Mecab {
     }
 }
 
+// SAFETY: `Send`と対立する性質はないはず。
+unsafe impl Send for Mecab {}
+
 impl Mecab {
     unsafe fn as_raw_ptr(&self) -> *mut open_jtalk_sys::Mecab {
         if self.0.is_none() {
diff --git a/crates/open_jtalk/src/njd.rs b/crates/open_jtalk/src/njd.rs
index 8928eb1..5dc7533 100644
--- a/crates/open_jtalk/src/njd.rs
+++ b/crates/open_jtalk/src/njd.rs
@@ -24,6 +24,9 @@ unsafe impl resources::Resource for Njd {
     }
 }
 
+// SAFETY: `Send`と対立する性質はないはず。
+unsafe impl Send for Njd {}
+
 impl Njd {
     pub(crate) unsafe fn as_raw_ptr(&self) -> *mut open_jtalk_sys::NJD {
         if self.0.is_none() {