diff --git a/scan_asn1string.c b/scan_asn1string.c
index c409859..c1ae632 100644
--- a/scan_asn1string.c
+++ b/scan_asn1string.c
@@ -4,9 +4,35 @@ size_t scan_asn1string(const char* src,const char* max,
 		       enum asn1_tagclass* tc,enum asn1_tagtype* tt,unsigned long* tag,
 		       const char** s,size_t* l) {
   size_t len,tmp;
-  if (!(len=scan_asn1tag(src,max,tc,tt,tag))) return 0;
-  if (!(tmp=scan_asn1length(src+len,max,l))) return 0;
+  if (!(len=scan_asn1tag(src,max,tc,tt,tag)))
+    return 0;
+  if (!(tmp=scan_asn1length(src+len,max,l)))
+    return 0;
   len+=tmp;
   *s=src+len;
   return len+*l;
 }
+
+#ifdef UNITTEST
+#include <string.h>
+#include <assert.h>
+
+#undef UNITTEST
+#include "scan_asn1tag.c"
+#include "scan_asn1tagint.c"
+#include "scan_asn1length.c"
+
+int main() {
+  char buf[100];
+  enum asn1_tagclass tc;
+  enum asn1_tagtype tt;
+  unsigned long tag;
+  const char* s;
+  size_t l;
+  strcpy(buf,"\x16\x05""fnord");
+  assert(scan_asn1string(buf,buf+7,&tc,&tt,&tag,&s,&l)==7 && tc==UNIVERSAL && tt==PRIMITIVE && tag==IA5String && s==buf+2 && l==5);
+  assert(scan_asn1string(buf,buf,&tc,&tt,&tag,&s,&l)==0);	// not enough input, first return 0
+  assert(scan_asn1string(buf,buf+6,&tc,&tt,&tag,&s,&l)==0);	// not enough input, second return 0
+  // we only care for 100% coverage of this file, the others have their own unit tests */
+}
+#endif