diff --git a/wolfssl/internal.h b/wolfssl/internal.h
index 01bbb0a4c..bdabad3cd 100644
--- a/wolfssl/internal.h
+++ b/wolfssl/internal.h
@@ -141,6 +141,8 @@
         /* do nothing */
 #elif defined(WOLFSSL_uTKERNEL2)
         /* do nothing */
+#elif defined(WOLFSSL_CMSIS_RTOS)
+    #include "cmsis_os.h"
 #elif defined(WOLFSSL_MDK_ARM)
     #if defined(WOLFSSL_MDK5)
          #include "cmsis_os.h"