diff --git a/include/monitor/monitor.h b/include/monitor/monitor.h
index 06cfcd8f36..1e1d6d2269 100644
--- a/include/monitor/monitor.h
+++ b/include/monitor/monitor.h
@@ -44,6 +44,6 @@ AddfdInfo *monitor_fdset_add_fd(int fd, bool has_fdset_id, int64_t fdset_id,
 int monitor_fdset_get_fd(int64_t fdset_id, int flags);
 int monitor_fdset_dup_fd_add(int64_t fdset_id, int dup_fd);
 void monitor_fdset_dup_fd_remove(int dup_fd);
-int monitor_fdset_dup_fd_find(int dup_fd);
+int64_t monitor_fdset_dup_fd_find(int dup_fd);
 
 #endif /* MONITOR_H */
diff --git a/monitor.c b/monitor.c
index 5c5cbe254a..dce3496920 100644
--- a/monitor.c
+++ b/monitor.c
@@ -2604,7 +2604,7 @@ err:
     return -1;
 }
 
-static int monitor_fdset_dup_fd_find_remove(int dup_fd, bool remove)
+static int64_t monitor_fdset_dup_fd_find_remove(int dup_fd, bool remove)
 {
     MonFdset *mon_fdset;
     MonFdsetFd *mon_fdset_fd_dup;
@@ -2632,7 +2632,7 @@ err:
     return -1;
 }
 
-int monitor_fdset_dup_fd_find(int dup_fd)
+int64_t monitor_fdset_dup_fd_find(int dup_fd)
 {
     return monitor_fdset_dup_fd_find_remove(dup_fd, false);
 }
diff --git a/stubs/fdset.c b/stubs/fdset.c
index f3d9980b7e..67dd5e1d34 100644
--- a/stubs/fdset.c
+++ b/stubs/fdset.c
@@ -6,7 +6,7 @@ int monitor_fdset_dup_fd_add(int64_t fdset_id, int dup_fd)
     return -1;
 }
 
-int monitor_fdset_dup_fd_find(int dup_fd)
+int64_t monitor_fdset_dup_fd_find(int dup_fd)
 {
     return -1;
 }