diff --git a/src/writeout.c b/src/writeout.c
index 14ba41b925001549955ac5f4acffd901d16e541f..9aab771840e897e7aae02dc031a68d87cdb41340 100644
--- a/src/writeout.c
+++ b/src/writeout.c
@@ -108,7 +108,7 @@ void ourWriteOut(CURL *curl, const char *writeinfo)
   long longinfo;
   double doubleinfo;
 
-  while(*ptr) {
+  while(ptr && *ptr) {
     if('%' == *ptr) {
       if('%' == ptr[1]) {
         /* an escaped %-letter */