diff --git a/src/dh-gex.c b/src/dh-gex.c
index fc444d4b..3c8e5e87 100644
--- a/src/dh-gex.c
+++ b/src/dh-gex.c
@@ -409,6 +409,7 @@ static int ssh_retrieve_dhgroup_file(FILE *moduli,
     size_t line = 0;
     size_t best_nlines = 0;
 
+    *best_size = 0;
     for(;;) {
         line++;
         firstbyte = getc(moduli);