diff --git a/library/ripemd160.c b/library/ripemd160.c
index eed664f..ba97c1f 100644
--- a/library/ripemd160.c
+++ b/library/ripemd160.c
@@ -456,7 +456,7 @@
     int i, ret = 0;
     unsigned char output[20];
 
-    memset(output, 0, sizeof output);
+    memset(output, 0, sizeof(output));
 
     for (i = 0; i < TESTS; i++) {
         if (verbose != 0) {