diff --git a/mongoose.c b/mongoose.c
index 901c6324..27ec8c77 100644
--- a/mongoose.c
+++ b/mongoose.c
@@ -1983,7 +1983,7 @@ static void MD5Final(unsigned char digest[16], MD5_CTX *ctx) {
   MD5Transform(ctx->buf, (uint32_t *) ctx->in);
   byteReverse((unsigned char *) ctx->buf, 4);
   memcpy(digest, ctx->buf, 16);
-  memset((char *) ctx, 0, sizeof(ctx));
+  memset((char *) ctx, 0, sizeof(*ctx));
 }
 #endif // !HAVE_MD5