diff --git a/include/spdlog/sinks/async_sink.h b/include/spdlog/sinks/async_sink.h
index 0de171cf..a6a5306e 100644
--- a/include/spdlog/sinks/async_sink.h
+++ b/include/spdlog/sinks/async_sink.h
@@ -42,14 +42,14 @@ public:
     async_sink(async_sink &&) = default;
     async_sink &operator=(async_sink &&) = default;
 
-    void set_overflow_policy(overflow_policy policy) { overflow_policy_ = policy; }
-    [[nodiscard]] overflow_policy get_overflow_policy() const { return overflow_policy_; }
+    void set_overflow_policy(overflow_policy policy);
+    [[nodiscard]] overflow_policy get_overflow_policy() const;
 
-    [[nodiscard]] size_t get_overrun_counter() const { return q_->overrun_counter(); }
-    void reset_overrun_counter() const { q_->reset_overrun_counter(); }
+    [[nodiscard]] size_t get_overrun_counter() const;
+    void reset_overrun_counter() const;
 
-    [[nodiscard]] size_t get_discard_counter() const { return q_->discard_counter(); }
-    void reset_discard_counter() const { q_->reset_discard_counter(); }
+    [[nodiscard]] size_t get_discard_counter() const;
+    void reset_discard_counter() const;
 
 private:
     void sink_it_(const details::log_msg &msg) override;
diff --git a/src/sinks/async_sink.cpp b/src/sinks/async_sink.cpp
index 9736c620..21d19b0c 100644
--- a/src/sinks/async_sink.cpp
+++ b/src/sinks/async_sink.cpp
@@ -56,6 +56,37 @@ void async_sink<Mutex>::sink_it_(const details::log_msg &msg) {
     send_message_(async_log_msg::type::log, msg);
 }
 
+
+template <typename Mutex>
+void async_sink<Mutex>::set_overflow_policy(overflow_policy policy) {
+    overflow_policy_ = policy;
+}
+
+template <typename Mutex>
+typename async_sink<Mutex>::overflow_policy async_sink<Mutex>::get_overflow_policy() const {
+    return overflow_policy_;
+}
+
+template <typename Mutex>
+size_t async_sink<Mutex>::get_overrun_counter() const {
+    return q_->overrun_counter();
+}
+
+template <typename Mutex>
+void async_sink<Mutex>::reset_overrun_counter() const {
+    q_->reset_overrun_counter();
+}
+
+template <typename Mutex>
+size_t async_sink<Mutex>::get_discard_counter() const {
+    return q_->discard_counter();
+}
+
+template <typename Mutex>
+void async_sink<Mutex>::reset_discard_counter() const {
+    q_->reset_discard_counter();
+}
+
 template <typename Mutex>
 void async_sink<Mutex>::flush_() {
     send_message_(async_log_msg::type::flush, details::log_msg());