diff --git a/library/gcm.c b/library/gcm.c
index f1a43af..08435f9 100644
--- a/library/gcm.c
+++ b/library/gcm.c
@@ -129,7 +129,8 @@
     0x9180, 0x8da0, 0xa9c0, 0xb5e0
 };
 
-void gcm_mult( gcm_context *ctx, const unsigned char x[16], unsigned char output[16] )
+static void gcm_mult( gcm_context *ctx, const unsigned char x[16],
+                      unsigned char output[16] )
 {
     int i = 0;
     unsigned char z[16];