avoided compilation warnings on gcc 3.3.x systems

diff --git a/skeletons/ber_tlv_length.c b/skeletons/ber_tlv_length.c
index b3c1ceb..508bc39 100644
--- a/skeletons/ber_tlv_length.c
+++ b/skeletons/ber_tlv_length.c
@@ -87,7 +87,7 @@
 	 * Indefinite length!
 	 */
 	ASN_DEBUG("Skipping indefinite length");
-	for(skip = ll, (char *)ptr += ll, size -= ll;;) {
+	for(skip = ll, ptr = ((char *)ptr) + ll, size -= ll;;) {
 		ber_tlv_tag_t tag;
 
 		/* Fetch the tag */
@@ -95,7 +95,7 @@
 		if(tl <= 0) return tl;
 
 		ll = ber_skip_length(BER_TLV_CONSTRUCTED(ptr),
-			(char *)ptr + tl, size - tl);
+			((char *)ptr) + tl, size - tl);
 		if(ll <= 0) return ll;
 
 		skip += tl + ll;
@@ -109,7 +109,7 @@
 		&& ((uint8_t *)ptr)[1] == 0)
 			return skip;
 
-		(char *)ptr  += tl + ll;
+		ptr = ((char *)ptr) + tl + ll;
 		size -= tl + ll;
  	}