diff --git a/library/entropy.c b/library/entropy.c
index 468ef03..9fc11a7 100644
--- a/library/entropy.c
+++ b/library/entropy.c
@@ -85,8 +85,8 @@
 /*
  * Entropy accumulator update
  */
-int entropy_update( entropy_context *ctx, unsigned char source_id,
-                    const unsigned char *data, size_t len )
+static int entropy_update( entropy_context *ctx, unsigned char source_id,
+                           const unsigned char *data, size_t len )
 {
     unsigned char header[2];
     unsigned char tmp[ENTROPY_BLOCK_SIZE];