diff --git a/skeletons/per_support.c b/skeletons/per_support.c
index 4e38c1a..9153e58 100644
--- a/skeletons/per_support.c
+++ b/skeletons/per_support.c
@@ -161,30 +161,36 @@
 }
 
 /*
- * Get the length "n" from the stream.
+ * X.691-201508 #10.9 General rules for encoding a length determinant.
+ * Get the optionally constrained length "n" from the stream.
  */
 ssize_t
 uper_get_length(asn_per_data_t *pd, int ebits, int *repeat) {
-	ssize_t value;
+    ssize_t value;
 
-	*repeat = 0;
+    *repeat = 0;
 
-	if(ebits >= 0) return per_get_few_bits(pd, ebits);
+    /* #11.9.4.1 Encoding if constrained (according to effective bits) */
+    if(ebits >= 0 && ebits <= 16) {
+        return per_get_few_bits(pd, ebits);
+    }
 
 	value = per_get_few_bits(pd, 8);
-	if(value < 0) return -1;
-	if((value & 128) == 0)	/* #10.9.3.6 */
-		return (value & 0x7F);
-	if((value & 64) == 0) {	/* #10.9.3.7 */
-		value = ((value & 63) << 8) | per_get_few_bits(pd, 8);
-		if(value < 0) return -1;
-		return value;
-	}
-	value &= 63;	/* this is "m" from X.691, #10.9.3.8 */
-	if(value < 1 || value > 4)
-		return -1;
-	*repeat = 1;
-	return (16384 * value);
+    if((value & 0x80) == 0) { /* #11.9.3.6 */
+        return (value & 0x7F);
+    } else if((value & 0x40) == 0) { /* #11.9.3.7 */
+        /* bit 8 ... set to 1 and bit 7 ... set to zero */
+        value = ((value & 0x3f) << 8) | per_get_few_bits(pd, 8);
+        return value; /* potential -1 from per_get_few_bits passes through. */
+    } else if(value < 0) {
+        return -1;
+    }
+    value &= 0x3f; /* this is "m" from X.691, #11.9.3.8 */
+    if(value < 1 || value > 4) {
+        return -1; /* Prohibited by #11.9.3.8 */
+    }
+    *repeat = 1;
+    return (16384 * value);
 }
 
 /*