diff --git a/src/asn1helpers.c b/src/asn1helpers.c
index 638cdb6..8ce9bf4 100644
--- a/src/asn1helpers.c
+++ b/src/asn1helpers.c
@@ -73,7 +73,7 @@
 	}
 
 	if (len < 0)
-		len = strlen(str);
+		len = strlen((char*)str);
 
 	buf = MALLOC(len);
 	if (!buf) {