diff --git a/system/lib/compiler-rt/lib/sanitizer_common/sanitizer_platform_limits_posix.h b/system/lib/compiler-rt/lib/sanitizer_common/sanitizer_platform_limits_posix.h
index 1b600798c79fc..4397a30319664 100644
--- a/system/lib/compiler-rt/lib/sanitizer_common/sanitizer_platform_limits_posix.h
+++ b/system/lib/compiler-rt/lib/sanitizer_common/sanitizer_platform_limits_posix.h
@@ -869,7 +869,7 @@ struct __sanitizer_pollfd {
   short revents;
 };
 
-#  if SANITIZER_ANDROID || SANITIZER_APPLE
+#  if SANITIZER_ANDROID || SANITIZER_APPLE || SANITIZER_EMSCRIPTEN
 typedef unsigned __sanitizer_nfds_t;
 #  else
 typedef unsigned long __sanitizer_nfds_t;
diff --git a/system/lib/libc/musl/include/poll.h b/system/lib/libc/musl/include/poll.h
index 272dc34a89e50..0cb10863bd155 100644
--- a/system/lib/libc/musl/include/poll.h
+++ b/system/lib/libc/musl/include/poll.h
@@ -26,7 +26,8 @@ extern "C" {
 #define POLLRDHUP  0x2000
 #endif
 
-typedef unsigned long nfds_t;
+// XXX Emscripten: nfds_t is kept 32-bit even on wasm64.
+typedef unsigned int nfds_t;
 
 struct pollfd {
 	int fd;