diff --git a/.github/workflows/ci.yml b/.github/workflows/ci.yml
index a99cf3c..2b5006a 100644
--- a/.github/workflows/ci.yml
+++ b/.github/workflows/ci.yml
@@ -398,7 +398,7 @@ jobs:
         run: emcc -v
       - name: build
         run: |
-          emcmake cmake -B build
+          emcmake cmake -B build -DBUILD_QJS_LIBC=ON
           emmake make -C build qjs_wasm -j$(getconf _NPROCESSORS_ONLN)
       - name: result
         run: ls -lh build
diff --git a/quickjs-libc.c b/quickjs-libc.c
index 6dbe501..a7b334f 100644
--- a/quickjs-libc.c
+++ b/quickjs-libc.c
@@ -3035,15 +3035,19 @@ static int my_execvpe(const char *filename, char **argv, char **envp)
     return -1;
 }
 
-static js_once_t js_os_exec_once = JS_ONCE_INIT;
-
 static void (*js_os_exec_closefrom)(int);
 
+#if !defined(EMSCRIPTEN) && !defined(__wasi__)
+
+static js_once_t js_os_exec_once = JS_ONCE_INIT;
+
 static void js_os_exec_once_init(void)
 {
     js_os_exec_closefrom = dlsym(RTLD_DEFAULT, "closefrom");
 }
 
+#endif
+
 /* exec(args[, options]) -> exitcode */
 static JSValue js_os_exec(JSContext *ctx, JSValue this_val,
                           int argc, JSValue *argv)
@@ -3163,9 +3167,11 @@ static JSValue js_os_exec(JSContext *ctx, JSValue this_val,
         }
     }
 
+#if !defined(EMSCRIPTEN) && !defined(__wasi__)
     // should happen pre-fork because it calls dlsym()
     // and that's not an async-signal-safe function
     js_once(&js_os_exec_once, js_os_exec_once_init);
+#endif
 
     pid = fork();
     if (pid < 0) {