diff --git a/scan_asn1length.c b/scan_asn1length.c
index 9e20fae..7dbd4a9 100644
--- a/scan_asn1length.c
+++ b/scan_asn1length.c
@@ -12,17 +12,66 @@ size_t scan_asn1length(const char* src,const char* max,size_t* value) {
   } else {
     /* Highest bit set: lower 7 bits is the length of the length value in bytes. */
     c&=0x7f;
-    if (!c) return 0;		/* length 0x80 means indefinite length encoding, not supported here */
+    if (!c)
+      return 0;		/* length 0x80 means indefinite length encoding, not supported here */
     l=(unsigned char)src[1];
-    if (l==0) return 0;		/* not minimally encoded: 0x81 0x00 instead of 0x00 */
-    if (c>sizeof(l)) return 0;	/* too many bytes, does not fit into target integer type */
-    if (c+1>len) return 0;	/* not enough data in input buffer */
+    if (l==0)
+      return 0;		/* not minimally encoded: 0x81 0x00 instead of 0x00 */
+    if (c>sizeof(l))
+      return 0;		/* too many bytes, does not fit into target integer type */
+    if (c+1>len)
+      return 0;		/* not enough data in input buffer */
     for (i=2; i<=c; ++i)
       l=l*256+(unsigned char)src[i];
-    if (l<0x7f) return 0;	/* not minimally encoded: 0x81 0x70 instead of 0x70 */
+    if (l<0x7f)
+      return 0;		/* not minimally encoded: 0x81 0x70 instead of 0x70 */
   }
-  if (l>len-i) return 0;	/* if the length would not fit into the buffer, return 0 */
+  if (l>len-i)
+    return 0;		/* if the length would not fit into the buffer, return 0 */
   *value=l;
   return i;
 }
 
+#ifdef UNITTEST
+#include <assert.h>
+#include <string.h>
+
+int main() {
+  char buf[10];
+  unsigned long l;
+  /* empty input */
+  assert(scan_asn1length(buf,buf,&l)==0);
+  /* regular 1-byte encoding */
+  strcpy(buf,"\x23");
+  assert(scan_asn1length(buf,buf+1,&l)==0);	// length fits but value doesn't
+  assert(scan_asn1length(buf,buf+0x23,&l)==0);	// length fits but value doesn't
+  assert(scan_asn1length(buf,buf+0x24,&l)==1 && l==0x23);	// OK
+  /* not minimally encoded */
+  strcpy(buf,"\x81\x23");	// not minimal, should have been "\x23"
+  assert(scan_asn1length(buf,buf+10,&l)==0);
+  /* indefinite length encoding not supported */
+  strcpy(buf,"\x80");
+  assert(scan_asn1length(buf,buf+1,&l)==0);
+  /* regular 2-byte encoding */
+  strcpy(buf,"\x81\x97");
+  assert(scan_asn1length(buf,buf+2,&l)==0);	// length fits but value doesn't
+  assert(scan_asn1length(buf,buf+255,&l)==2 && l==0x97);
+  /* non-minimal multi-byte */
+  memcpy(buf,"\x82\x00\x97",3);	// not minimal, should have been "\x81\x97"
+  assert(scan_asn1length(buf,buf+3,&l)==0);
+  /* value not representable */
+  memcpy(buf,"\x89\x01\x02\x03\x04\x05\x06\x07\x08\x09",10);	// can't fit 9 bytes into long
+  // this will also fail the "length bytes fit in input buffer"
+  assert(scan_asn1length(buf,buf+10,&l)==0);
+  /* value does not fit in input buffer */
+  memcpy(buf,"\x81\x80",2);	// length 0x80
+  assert(scan_asn1length(buf,buf+10,&l)==0);	// length fits, value doesn't
+  assert(scan_asn1length(buf,buf+0x90,&l)==2 && l==0x80);	// OK
+  assert(scan_asn1length(buf,buf+1,&l)==0);	// length doesn't fit
+  // three byte encoding
+  memcpy(buf,"\x82\x80\x00",3);	// length 0x8000
+  assert(scan_asn1length(buf,buf+10,&l)==0);	// length fits, value doesn't
+  assert(scan_asn1length(buf,buf+0x8010,&l)==3 && l==0x8000);	// OK
+  assert(scan_asn1length(buf,buf+2,&l)==0);	// length doesn't fit
+}
+#endif
diff --git a/scan_asn1tag.c b/scan_asn1tag.c
index e124950..21b7782 100644
--- a/scan_asn1tag.c
+++ b/scan_asn1tag.c
@@ -7,7 +7,8 @@
 #endif
 
 size_t scan_asn1tag(const char* src,const char* max,enum asn1_tagclass* tc,enum asn1_tagtype* tt,unsigned long* tag) {
-  if (max<=src) return 0;
+  if (max<=src)
+    return 0;
   *tc=(*src&0xC0);
   *tt=(*src&0x20);
 /* The lower 5 bits are the tag, unless it's 0x1f, in which case the
@@ -15,6 +16,8 @@ size_t scan_asn1tag(const char* src,const char* max,enum asn1_tagclass* tc,enum
  * in the sequence is marked by a cleared high bit */
   if ((*src & 0x1f) == 0x1f) {
     size_t res=scan_asn1tagint(src+1,max,tag);
+    if (res && *tag < 0x1f)	// non-minimal encoding
+      return 0;
     return res+!!res;	/* add 1 unless it's 0, then leave 0 */
   } else {
     *tag=*src&0x1f;
@@ -30,7 +33,28 @@ int main() {
   enum asn1_tagclass tc;
   enum asn1_tagtype tt;
   unsigned long tag;
-  char buf[10];
+  char buf[15];
+  assert(scan_asn1tag(buf,buf,&tc,&tt,&tag)==0);	// empty input
   strcpy(buf,"\x01"); assert(scan_asn1tag(buf,buf+10,&tc,&tt,&tag)==1 && tc==UNIVERSAL && tt==PRIMITIVE && tag==BOOLEAN);
+  /* incomplete input */
+  strcpy(buf,"\x1f"); assert(scan_asn1tag(buf,buf+1,&tc,&tt,&tag)==0);
+  /* long-form encoding when short-form would have sufficed */
+  strcpy(buf,"\x1f\x1e");
+  assert(scan_asn1tag(buf,buf+10,&tc,&tt,&tag)==0);
+  /* OK */
+  strcpy(buf,"\x1f\x1f");
+  assert(scan_asn1tag(buf,buf+10,&tc,&tt,&tag)==2 && tc==UNIVERSAL && tt==PRIMITIVE && tag==0x1f);
+  /* non-minimal encoding */
+  strcpy(buf,"\x1f\x80\x01");
+  assert(scan_asn1tag(buf,buf+10,&tc,&tt,&tag)==0);
+  /* incomplete encoding */
+  assert(scan_asn1tag(buf,buf+2,&tc,&tt,&tag)==0);
+  strcpy(buf,"\x1f\x81\x00");
+  assert(scan_asn1tag(buf,buf+10,&tc,&tt,&tag)==3 && tc==UNIVERSAL && tt==PRIMITIVE && tag==0x80);
+  /* value not representable */
+  memcpy(buf,"\x1f\xff\xff\xff\xff\xff\xff\xff\xff\xff\x7f",11);
+  assert(scan_asn1tag(buf,buf+12,&tc,&tt,&tag)==0);
+  memcpy(buf,"\x1f\x8f\xff\xff\xff\x7f",7);
+  assert(scan_asn1tag(buf,buf+10,&tc,&tt,&tag)==6 && tc==UNIVERSAL && tt==PRIMITIVE && tag==0xffffffff);
 }
 #endif
diff --git a/scan_asn1tagint.c b/scan_asn1tagint.c
index 8711136..3050688 100644
--- a/scan_asn1tagint.c
+++ b/scan_asn1tagint.c
@@ -4,12 +4,15 @@ size_t scan_asn1tagint(const char* src,const char* bounds,unsigned long* val) {
   const char* orig=src;
   unsigned long l=0;
   if (src>=bounds ||				/* empty input */
-      (unsigned char)src[0]==0x80) return 0;	/* catch non-minimal encoding */
+      (unsigned char)src[0]==0x80)
+    return 0;	/* catch non-minimal encoding */
   for (;; ++src) {
     if (src>=bounds ||				/* incomplete input */
-        l>>(sizeof(l)*8-7)) return 0;		/* catch integer overflow */
+        l>>(sizeof(l)*8-7))
+      return 0;		/* catch integer overflow */
     l=l*128+(*src&0x7F);
-    if (!(*src&0x80)) break;
+    if (!(*src&0x80))
+      break;
   }
   *val=l;
   return src-orig+1;