diff --git a/include/polarssl/entropy.h b/include/polarssl/entropy.h
index 6dea79a..53bce41 100644
--- a/include/polarssl/entropy.h
+++ b/include/polarssl/entropy.h
@@ -38,6 +38,7 @@
 
 #define POLARSSL_ERR_ENTROPY_SOURCE_FAILED                 -0x003C  /**< Critical entropy source failure. */
 #define POLARSSL_ERR_ENTROPY_MAX_SOURCES                   -0x003E  /**< No more sources can be added. */
+#define POLARSSL_ERR_ENTROPY_NO_SOURCES_DEFINED            -0x0040  /**< No sources have been added to poll. */
 
 #define ENTROPY_MAX_SOURCES     20      /**< Maximum number of sources supported */
 #define ENTROPY_MAX_GATHER      128     /**< Maximum amount requested from entropy sources */
@@ -104,7 +105,7 @@
  * \param threshold Minimum required from source before entropy is released
  *                  ( with entropy_func() )
  *
- * \return          0 is successful or POLARSSL_ERR_ENTROPY_MAX_SOURCES
+ * \return          0 if successful or POLARSSL_ERR_ENTROPY_MAX_SOURCES
  */
 int entropy_add_source( entropy_context *ctx,
                         f_source_ptr f_source, void *p_source,