diff --git a/lib/asn1/gen.c b/lib/asn1/gen.c
index b481e1d14..9e5f086db 100644
--- a/lib/asn1/gen.c
+++ b/lib/asn1/gen.c
@@ -763,6 +763,27 @@ define_type (int level, const char *name, const char *basename, Type *t, int typ
 	Member *m;
 	Type i;
 	struct range range = { 0, UINT_MAX };
+        size_t max_memno = 0;
+        size_t bitset_size;
+
+        /*
+         * range.max implies the size of the base unsigned integer used for the
+         * bitfield members.  If it's less than or equal to UINT_MAX, then that
+         * will be unsigned int, otherwise it will be uint64_t.
+         *
+         * We could just use uint64_t, yes, but for now, and in case that any
+         * projects were exposing the BIT STRING types' C representations in
+         * ABIs prior to this compiler supporting BIT STRING with larger
+         * members, we stick to this.
+         */
+        ASN1_TAILQ_FOREACH(m, t->members, members) {
+            if (m->val > max_memno)
+                max_memno = m->val;
+        }
+        if (max_memno > 63)
+            range.max = INT64_MAX;
+        else
+            range.max = 1LU << max_memno;
 
 	i.type = TInteger;
 	i.range = &range;
@@ -780,10 +801,13 @@ define_type (int level, const char *name, const char *basename, Type *t, int typ
 	    ASN1_TAILQ_FOREACH(m, t->members, members) {
 		char *n = NULL;
 
-		/* pad unused */
+		/*
+                 * pad unused bits beween declared members (hopefully this
+                 * forces the compiler to give us an obvious layout)
+                 */
 		while (pos < m->val) {
 		    if (asprintf (&n, "_unused%d:1", pos) < 0 || n == NULL)
-			errx(1, "malloc");
+			err(1, "malloc");
 		    define_type (level + 1, n, newbasename, &i, FALSE, FALSE);
 		    free(n);
 		    pos++;
@@ -797,8 +821,13 @@ define_type (int level, const char *name, const char *basename, Type *t, int typ
 		n = NULL;
 		pos++;
 	    }
-	    /* pad to 32 elements */
-	    while (pos < 32) {
+	    /* pad unused tail (ditto) */
+            bitset_size = max_memno;
+            if (max_memno > 31)
+                bitset_size += 64 - (max_memno % 64);
+            else
+                bitset_size = 32;
+	    while (pos < bitset_size) {
 		char *n = NULL;
 		if (asprintf (&n, "_unused%d:1", pos) < 0 || n == NULL)
 		    errx(1, "malloc");
diff --git a/lib/asn1/gen_decode.c b/lib/asn1/gen_decode.c
index 650017fa6..6c9f6e5aa 100644
--- a/lib/asn1/gen_decode.c
+++ b/lib/asn1/gen_decode.c
@@ -354,7 +354,7 @@ decode_type (const char *name, const Type *t, int optional,
 	    break;
 
 	fprintf(codefile, "{\n");
-	fprintf(codefile, "unsigned int members = 0;\n");
+	fprintf(codefile, "uint64_t members = 0;\n");
 	fprintf(codefile, "while(len > 0) {\n");
 	fprintf(codefile,
 		"Der_class class;\n"
@@ -384,7 +384,7 @@ decode_type (const char *name, const Type *t, int optional,
 	    decode_type (s, m->type, 0, forwstr, m->gen_name, NULL, depth + 1);
 	    free (s);
 
-	    fprintf(codefile, "members |= (1 << %d);\n", memno);
+	    fprintf(codefile, "members |= (1LU << %u);\n", memno);
 	    memno++;
 	    fprintf(codefile, "break;\n");
 	}
@@ -400,7 +400,7 @@ decode_type (const char *name, const Type *t, int optional,
 
 	    if (asprintf (&s, "%s->%s", name, m->gen_name) < 0 || s == NULL)
 		errx(1, "malloc");
-	    fprintf(codefile, "if((members & (1 << %d)) == 0)\n", memno);
+	    fprintf(codefile, "if((members & (1LU << %u)) == 0)\n", memno);
 	    if(m->optional)
 		fprintf(codefile, "%s = NULL;\n", s);
 	    else if(m->defval)
diff --git a/lib/asn1/gen_glue.c b/lib/asn1/gen_glue.c
index 773ce787d..a7d90e368 100644
--- a/lib/asn1/gen_glue.c
+++ b/lib/asn1/gen_glue.c
@@ -43,17 +43,17 @@ generate_2int (const Type *t, const char *gen_name)
     Member *m;
 
     fprintf (headerfile,
-	     "unsigned %s2int(%s);\n",
+	     "uint64_t %s2int(%s);\n",
 	     gen_name, gen_name);
 
     fprintf (codefile,
-	     "unsigned %s2int(%s f)\n"
+	     "uint64_t %s2int(%s f)\n"
 	     "{\n"
-	     "unsigned r = 0;\n",
+	     "uint64_t r = 0;\n",
 	     gen_name, gen_name);
 
     ASN1_TAILQ_FOREACH(m, t->members, members) {
-	fprintf (codefile, "if(f.%s) r |= (1U << %d);\n",
+	fprintf (codefile, "if(f.%s) r |= (1LU << %d);\n",
 		 m->gen_name, m->val);
     }
     fprintf (codefile, "return r;\n"
@@ -66,11 +66,11 @@ generate_int2 (const Type *t, const char *gen_name)
     Member *m;
 
     fprintf (headerfile,
-	     "%s int2%s(unsigned);\n",
+	     "%s int2%s(uint64_t);\n",
 	     gen_name, gen_name);
 
     fprintf (codefile,
-	     "%s int2%s(unsigned n)\n"
+	     "%s int2%s(uint64_t n)\n"
 	     "{\n"
 	     "\t%s flags;\n\n"
 	     "\tmemset(&flags, 0, sizeof(flags));\n\n",
@@ -114,7 +114,7 @@ generate_units (const Type *t, const char *gen_name)
     if(t->members) {
 	ASN1_TAILQ_FOREACH_REVERSE(m, t->members, memhead, members) {
 	    fprintf (codefile,
-		     "\t{\"%s\",\t1U << %d},\n", m->name, m->val);
+		     "\t{\"%s\",\t1LU << %d},\n", m->name, m->val);
 	}
     }
 
@@ -143,14 +143,21 @@ generate_glue (const Type *t, const char *gen_name)
     case TTag:
 	generate_glue(t->subtype, gen_name);
 	break;
-    case TBitString :
-	if (!ASN1_TAILQ_EMPTY(t->members)) {
-	    generate_2int (t, gen_name);
-	    generate_int2 (t, gen_name);
-	    if (parse_units_flag)
-		generate_units (t, gen_name);
-	}
+    case TBitString : {
+        Member *m;
+
+        if (ASN1_TAILQ_EMPTY(t->members))
+            break;
+        ASN1_TAILQ_FOREACH(m, t->members, members) {
+            if (m->val > 63)
+                return;
+        }
+        generate_2int (t, gen_name);
+        generate_int2 (t, gen_name);
+        if (parse_units_flag)
+            generate_units (t, gen_name);
 	break;
+    }
     default :
 	break;
     }
diff --git a/lib/asn1/test.asn1 b/lib/asn1/test.asn1
index 3b70a02cd..7546ed744 100644
--- a/lib/asn1/test.asn1
+++ b/lib/asn1/test.asn1
@@ -188,6 +188,21 @@ TESTBitString ::= BIT STRING {
 	      thirtyone(31)
 }
 
+TESTBitString64 ::= BIT STRING {
+	      zero(0),
+	      eight(8),
+	      thirtyone(31),
+	      thirtytwo(32),
+	      sixtythree(63)
+}
+
+TESTLargeBitString ::= BIT STRING {
+	      zero(0),
+	      eight(8),
+	      thirtyone(31),
+	      onehundredtwenty(120)
+}
+
 TESTMechType::= OBJECT IDENTIFIER
 TESTMechTypeList ::= SEQUENCE OF TESTMechType
 
diff --git a/lib/roken/parse_units.h b/lib/roken/parse_units.h
index 636690595..0cb5f5a9a 100644
--- a/lib/roken/parse_units.h
+++ b/lib/roken/parse_units.h
@@ -51,7 +51,7 @@
 
 struct units {
     const char *name;
-    unsigned mult;
+    unsigned long long mult;
 };
 
 ROKEN_LIB_FUNCTION int ROKEN_LIB_CALL