diff --git a/java/io/nayuki/qrcodegen/BitBuffer.java b/java/io/nayuki/qrcodegen/BitBuffer.java
index 4d8c5d7..722a07f 100644
--- a/java/io/nayuki/qrcodegen/BitBuffer.java
+++ b/java/io/nayuki/qrcodegen/BitBuffer.java
@@ -97,6 +97,7 @@ public final class BitBuffer implements Cloneable {
 	 * to this sequence. Requires 0 &le; val &lt; 2<sup>len</sup>.
 	 * @param val the value to append
 	 * @param len the number of low bits in the value to take
+	 * @throws IllegalArgumentException if the value or number of bits is out of range
 	 * @throws IllegalStateException if appending the data
 	 * would make bitLength exceed Integer.MAX_VALUE
 	 */
diff --git a/rust/src/lib.rs b/rust/src/lib.rs
index 3f42530..bb57352 100644
--- a/rust/src/lib.rs
+++ b/rust/src/lib.rs
@@ -1067,7 +1067,7 @@ impl BitBuffer {
 	// Appends the given number of low bits of the given value
 	// to this sequence. Requires 0 <= len <= 31 and 0 <= val < 2^len.
 	pub fn append_bits(&mut self, val: u32, len: u8) {
-		assert!(len < 32 && (val >> len) == 0 || len == 32, "Value out of range");
+		assert!(len <= 31 && (val >> len) == 0, "Value out of range");
 		self.0.extend((0 .. len as i32).rev().map(|i| get_bit(val, i)));  // Append bit by bit
 	}
 }