diff --git a/fmt/fmt_asn1derlength.c b/fmt/fmt_asn1derlength.c
index 2ab3c91..263d473 100644
--- a/fmt/fmt_asn1derlength.c
+++ b/fmt/fmt_asn1derlength.c
@@ -13,11 +13,11 @@ size_t fmt_asn1derlength(char* dest,unsigned long long l) {
     if (!(l>>(i*8)))
       break;
   if (dest) {
-    int j=i;
-    *dest=0x80+i; ++dest;
+    size_t j=i;
+    *dest=(char)(0x80+i); ++dest;
     while (j) {
       --j;
-      *dest=((l>>(j*8))&0xff);
+      *dest=(char)((l>>(j*8))&0xff);
       ++dest;
     }
   }
diff --git a/fmt/fmt_asn1dertag.c b/fmt/fmt_asn1dertag.c
index dc5452f..c91f506 100644
--- a/fmt/fmt_asn1dertag.c
+++ b/fmt/fmt_asn1dertag.c
@@ -8,7 +8,7 @@ size_t fmt_asn1dertag(char* dest,unsigned long long l) {
   unsigned long long t;
   for (t=l, n=1; t>0x7f; t>>=7) ++n;
   for (i=0; i<n; ++i) {
-    if (dest) dest[n-i-1]=((i!=0)<<7) | (l&0x7f);
+    if (dest) dest[n-i-1]=(char)(((i!=0)<<7) | (char)(l&0x7f));
     l>>=7;
   }
   return i;