diff --git a/library/threading.c b/library/threading.c
index 0496b97..7231f2f 100644
--- a/library/threading.c
+++ b/library/threading.c
@@ -35,8 +35,9 @@
 
 #include "mbedtls/threading.h"
 
-#if !defined(_WIN32) && (defined(unix) || defined(__unix) || \
-    defined(__unix__) || (defined(__APPLE__) && defined(__MACH__)))
+#if !defined(_WIN32) && !defined(__IAR_SYSTEMS_ICC__) && (defined(unix) || \
+    defined(__unix) || defined(__unix__) || (defined(__APPLE__) && \
+    defined(__MACH__)))
 #include <unistd.h>
 #if !defined(_POSIX_VERSION) || 200112L > _POSIX_THREAD_SAFE_FUNCTIONS
 /*
@@ -48,7 +49,8 @@
  */
 #define THREADING_USE_GMTIME
 #endif /* !_POSIX_VERSION || 200112L > _POSIX_THREAD_SAFE_FUNCTIONS */
-#endif /* !_WIN32 && (unix || __unix || __unix__ || (__APPLE__ && __MACH__)) */
+#endif /* !_WIN32 && !__IAR_SYSTEMS_ICC__ && (unix || __unix || __unix__ ||
+        * (__APPLE__ && __MACH__)) */
 
 #if defined(MBEDTLS_THREADING_PTHREAD)
 static void threading_mutex_init_pthread( mbedtls_threading_mutex_t *mutex )