diff --git a/libtransmission/watchdir-common.h b/libtransmission/watchdir-common.h
index 34c6dab81..f3d807848 100644
--- a/libtransmission/watchdir-common.h
+++ b/libtransmission/watchdir-common.h
@@ -12,14 +12,15 @@
 #error only the libtransmission watchdir module should #include this header.
 #endif
 
-struct tr_ptrArray;
+#include <string>
+#include <unordered_set>
 
 typedef struct tr_watchdir_backend
 {
     void (*free_func)(struct tr_watchdir_backend*);
 } tr_watchdir_backend;
 
-#define BACKEND_DOWNCAST(b) ((tr_watchdir_backend*)(b))
+#define BACKEND_DOWNCAST(b) (reinterpret_cast<tr_watchdir_backend*>(b))
 
 /* ... */
 
@@ -31,7 +32,7 @@ struct event_base* tr_watchdir_get_event_base(tr_watchdir_t handle);
 
 void tr_watchdir_process(tr_watchdir_t handle, char const* name);
 
-void tr_watchdir_scan(tr_watchdir_t handle, struct tr_ptrArray* dir_entries);
+void tr_watchdir_scan(tr_watchdir_t handle, std::unordered_set<std::string>* dir_entries);
 
 /* ... */
 
diff --git a/libtransmission/watchdir-generic.cc b/libtransmission/watchdir-generic.cc
index 1a5b2d606..b51fca0e6 100644
--- a/libtransmission/watchdir-generic.cc
+++ b/libtransmission/watchdir-generic.cc
@@ -7,6 +7,8 @@
  */
 
 #include <errno.h>
+#include <string>
+#include <unordered_set>
 
 #include <event2/event.h>
 
@@ -14,7 +16,6 @@
 
 #include "transmission.h"
 #include "log.h"
-#include "ptrarray.h"
 #include "tr-assert.h"
 #include "utils.h"
 #include "watchdir.h"
@@ -37,10 +38,10 @@ typedef struct tr_watchdir_generic
     tr_watchdir_backend base;
 
     struct event* event;
-    tr_ptrArray dir_entries;
+    std::unordered_set<std::string> dir_entries;
 } tr_watchdir_generic;
 
-#define BACKEND_UPCAST(b) ((tr_watchdir_generic*)(b))
+#define BACKEND_UPCAST(b) (reinterpret_cast<tr_watchdir_generic*>(b))
 
 /* Non-static and mutable for unit tests. default to 10 sec. */
 auto tr_watchdir_generic_interval = timeval{ 10, 0 };
@@ -77,16 +78,12 @@ static void tr_watchdir_generic_free(tr_watchdir_backend* backend_base)
         event_free(backend->event);
     }
 
-    tr_ptrArrayDestruct(&backend->dir_entries, &tr_free);
-
-    tr_free(backend);
+    delete backend;
 }
 
 tr_watchdir_backend* tr_watchdir_generic_new(tr_watchdir_t handle)
 {
-    tr_watchdir_generic* backend;
-
-    backend = tr_new0(tr_watchdir_generic, 1);
+    auto* backend = new tr_watchdir_generic{};
     backend->base.free_func = &tr_watchdir_generic_free;
 
     if ((backend
diff --git a/libtransmission/watchdir-kqueue.cc b/libtransmission/watchdir-kqueue.cc
index 4806fe91a..0ecc4dce3 100644
--- a/libtransmission/watchdir-kqueue.cc
+++ b/libtransmission/watchdir-kqueue.cc
@@ -8,6 +8,8 @@
 
 #include <errno.h>
 #include <string.h> /* strcmp() */
+#include <string>
+#include <unordered_set>
 
 #include <fcntl.h> /* open() */
 #include <unistd.h> /* close() */
@@ -25,7 +27,6 @@
 
 #include "transmission.h"
 #include "log.h"
-#include "ptrarray.h"
 #include "tr-assert.h"
 #include "utils.h"
 #include "watchdir.h"
@@ -50,10 +51,10 @@ typedef struct tr_watchdir_kqueue
     int kq;
     int dirfd;
     struct event* event;
-    tr_ptrArray dir_entries;
+    std::unordered_set<std::string> dir_entries;
 } tr_watchdir_kqueue;
 
-#define BACKEND_UPCAST(b) ((tr_watchdir_kqueue*)(b))
+#define BACKEND_UPCAST(b) (reinterpret_cast<tr_watchdir_kqueue*>(b))
 
 #define KQUEUE_WATCH_MASK (NOTE_WRITE | NOTE_EXTEND)
 
@@ -108,18 +109,15 @@ static void tr_watchdir_kqueue_free(tr_watchdir_backend* backend_base)
         close(backend->dirfd);
     }
 
-    tr_ptrArrayDestruct(&backend->dir_entries, &tr_free);
-
-    tr_free(backend);
+    delete backend;
 }
 
 tr_watchdir_backend* tr_watchdir_kqueue_new(tr_watchdir_t handle)
 {
     char const* const path = tr_watchdir_get_path(handle);
     struct kevent ke;
-    tr_watchdir_kqueue* backend;
 
-    backend = tr_new0(tr_watchdir_kqueue, 1);
+    auto* backend = new tr_watchdir_kqueue{};
     backend->base.free_func = &tr_watchdir_kqueue_free;
     backend->kq = -1;
     backend->dirfd = -1;
diff --git a/libtransmission/watchdir.cc b/libtransmission/watchdir.cc
index 000108000..8eb0411ad 100644
--- a/libtransmission/watchdir.cc
+++ b/libtransmission/watchdir.cc
@@ -328,12 +328,11 @@ void tr_watchdir_process(tr_watchdir_t handle, char const* name)
     }
 }
 
-void tr_watchdir_scan(tr_watchdir_t handle, tr_ptrArray* dir_entries)
+void tr_watchdir_scan(tr_watchdir_t handle, std::unordered_set<std::string>* dir_entries)
 {
     tr_sys_dir_t dir;
     char const* name;
-    auto new_dir_entries = tr_ptrArray{};
-    auto const name_compare_func = (PtrArrayCompareFunc)&strcmp;
+    auto new_dir_entries = std::unordered_set<std::string>{};
     tr_error* error = nullptr;
 
     if ((dir = tr_sys_dir_open(handle->path, &error)) == TR_BAD_SYS_DIR)
@@ -352,9 +351,10 @@ void tr_watchdir_scan(tr_watchdir_t handle, tr_ptrArray* dir_entries)
 
         if (dir_entries != nullptr)
         {
-            tr_ptrArrayInsertSorted(&new_dir_entries, tr_strdup(name), name_compare_func);
+            auto const namestr = std::string(name);
+            new_dir_entries.insert(namestr);
 
-            if (tr_ptrArrayFindSorted(dir_entries, name, name_compare_func) != nullptr)
+            if (dir_entries->count(namestr) != 0)
             {
                 continue;
             }
@@ -373,7 +373,6 @@ void tr_watchdir_scan(tr_watchdir_t handle, tr_ptrArray* dir_entries)
 
     if (dir_entries != nullptr)
     {
-        tr_ptrArrayDestruct(dir_entries, &tr_free);
         *dir_entries = new_dir_entries;
     }
 }
diff --git a/tests/libtransmission/watchdir-test.cc b/tests/libtransmission/watchdir-test.cc
index f294099a3..8a0194266 100644
--- a/tests/libtransmission/watchdir-test.cc
+++ b/tests/libtransmission/watchdir-test.cc
@@ -360,6 +360,8 @@ TEST_P(WatchDirTest, retry)
     processEvents();
     EXPECT_EQ(wd, wd_data.wd);
     EXPECT_EQ(test_file, wd_data.name);
+
+    tr_watchdir_free(wd);
 }
 
 INSTANTIATE_TEST_SUITE_P( //