diff --git a/wolfssl/wolfcrypt/wc_port.h b/wolfssl/wolfcrypt/wc_port.h
index 0cf0eea656..22be9351fa 100644
--- a/wolfssl/wolfcrypt/wc_port.h
+++ b/wolfssl/wolfcrypt/wc_port.h
@@ -59,7 +59,9 @@
 #endif /* WOLFSSL_LINUXKM */
 
 /* THREADING/MUTEX SECTION */
-#ifdef USE_WINDOWS_API
+#if defined(SINGLE_THREADED) && define(NO_FILESYSTEM)
+    /* No system headers required for build. */
+#elif defined(USE_WINDOWS_API)
     #if defined(WOLFSSL_PTHREADS)
         #include <pthread.h>
     #endif