diff --git a/src/os_win/thread.c b/src/os_win/thread.c
index 8fe6c73..d3505d6 100644
--- a/src/os_win/thread.c
+++ b/src/os_win/thread.c
@@ -190,13 +190,14 @@ int tss_set(tss_t key, void *val) {
 // Call once
 
 static BOOL _call_once_trampoline(PINIT_ONCE init_once, PVOID param, PVOID *ctx) {
-    void (*user_func)(void) = *ctx;
+    void (*user_func)(void) = param;
     user_func();
     return TRUE;
 }
 
 void call_once(once_flag *flag, void (*func)(void)) {
-    InitOnceExecuteOnce((void *)flag, _call_once_trampoline, NULL, (void **)&func);
+    void *funcp = func;
+    InitOnceExecuteOnce((void *)flag, _call_once_trampoline, funcp, NULL);
 }
 
 // Mutex functions
diff --git a/test/test_threads.c b/test/test_threads.c
index 9d11c8b..88129ce 100644
--- a/test/test_threads.c
+++ b/test/test_threads.c
@@ -2,7 +2,7 @@
 #include <threads.h>
 #include <stdatomic.h>
 
-#define N_THREADS 1
+#define N_THREADS 5
 
 _Thread_local int counter;
 once_flag flag = ONCE_FLAG_INIT;