diff --git a/include/mbedtls/entropy.h b/include/mbedtls/entropy.h
index a4fd0be..0ba30af 100644
--- a/include/mbedtls/entropy.h
+++ b/include/mbedtls/entropy.h
@@ -134,6 +134,14 @@
 }
 mbedtls_entropy_context;
 
+#if !defined(MBEDTLS_NO_PLATFORM_ENTROPY)
+/**
+ * \brief           Platform-specific entropy poll callback
+ */
+int mbedtls_platform_entropy_poll( void *data,
+                           unsigned char *output, size_t len, size_t *olen );
+#endif
+
 /**
  * \brief           Initialize the context
  *