diff --git a/lib/typeid.rb b/lib/typeid.rb
index 46484c8..0486817 100644
--- a/lib/typeid.rb
+++ b/lib/typeid.rb
@@ -54,6 +54,7 @@ def initialize(
     raise Error, "prefix must be lowercase ASCII characters" unless prefix.match?(/^[a-z]*$/)
     raise Error, "suffix must be #{SUFFIX_LENGTH} characters" unless suffix.length == SUFFIX_LENGTH
     raise Error, "suffix must only contain the letters in '#{TypeID::UUID::Base32::ALPHABET}'" unless suffix.chars.all? { |char| TypeID::UUID::Base32::ALPHABET.include?(char) }
+    raise Error, "suffix must start with a 0-7 digit to avoid overflows" unless ("0".."7").cover?(suffix.chars.first)
 
     @prefix = prefix
     @suffix = suffix
diff --git a/spec/invalid.yml b/spec/invalid.yml
index c1470a2..6a2870b 100644
--- a/spec/invalid.yml
+++ b/spec/invalid.yml
@@ -4,7 +4,7 @@
 # Each example contains an invalid TypeID string. Implementations are expected
 # to throw an error when attempting to parse/validate these strings.
 #
-# Last updated: 2023-06-29
+# Last updated: 2023-07-05
 
 - name: prefix-uppercase
   typeid: "PREFIX_00000000000000000000000000"
@@ -31,7 +31,7 @@
   description: "The prefix can't have any spaces"
 
 - name: prefix-64-chars
-  #          123456789 123456789 123456789 123456789 123456789 123456789 1234
+  #        123456789 123456789 123456789 123456789 123456789 123456789 1234
   typeid: "abcdefghijklmnopqrstuvwxyzabcdefghijklmnopqrstuvwxyzabcdefghijkl_00000000000000000000000000"
   description: "The prefix can't be 64 characters, it needs to be 63 characters or less"
 
@@ -81,3 +81,8 @@
   # This example would be valid if we were using the crockford hyphenation rules
   typeid: "prefix_123456789-0123456789-0123456"
   description: "The suffix can't ignore hyphens as in the crockford encoding"
+
+- name: suffix-overflow
+  # This is the first suffix that overflows into 129 bits
+  typeid: "prefix_8zzzzzzzzzzzzzzzzzzzzzzzzz"
+  description: "The should encode at most 128-bits"
diff --git a/spec/lib/typeid_spec.rb b/spec/lib/typeid_spec.rb
index 35f4a30..bf0bcfc 100644
--- a/spec/lib/typeid_spec.rb
+++ b/spec/lib/typeid_spec.rb
@@ -27,6 +27,12 @@
     it { is_expected.to eq string }
   end
 
+  describe ".nil" do
+    subject(:type_id) { TypeID.nil }
+
+    it { is_expected.to eq "00000000000000000000000000" }
+  end
+
   describe "#string" do
     it { is_expected.to eq "#{prefix}_#{suffix}" }
   end
diff --git a/spec/valid.yml b/spec/valid.yml
index 964c96f..8f63250 100644
--- a/spec/valid.yml
+++ b/spec/valid.yml
@@ -17,13 +17,13 @@
 # decoding and re-encoding the id, the result is the same as the original.
 #
 # In other words, the following property should always hold:
-# random_typeid: encode(decode(random_typeid))
+# random_typeid == encode(decode(random_typeid))
 #
 # Finally, while implementations should be able to decode the values below,
 # note that not all of them are UUIDv7s. When *generating* new random typeids,
 # implementations should always use UUIDv7s.
 #
-# Last updated: 2023-06-29
+# Last updated: 2023-07-05
 
 - name: nil
   typeid: "00000000000000000000000000"
@@ -50,6 +50,11 @@
   prefix: ""
   uuid: "00000000-0000-0000-0000-000000000020"
 
+- name: max-valid
+  typeid: "7zzzzzzzzzzzzzzzzzzzzzzzzz"
+  prefix: ""
+  uuid: "ffffffff-ffff-ffff-ffff-ffffffffffff"
+
 - name: valid-alphabet
   typeid: "prefix_0123456789abcdefghjkmnpqrs"
   prefix: "prefix"