diff --git a/lib/propane/code_point_range.rb b/lib/propane/code_point_range.rb
index 98a55e7..93930be 100644
--- a/lib/propane/code_point_range.rb
+++ b/lib/propane/code_point_range.rb
@@ -1,7 +1,7 @@
 class Propane
   class CodePointRange
 
-    MAX_CODE_POINT = 0xFFFFFFFF
+    MAX_CODE_POINT = 0x7FFFFFFF
 
     attr_reader :first
     attr_reader :last
diff --git a/spec/propane/code_point_range_spec.rb b/spec/propane/code_point_range_spec.rb
index 162d7cf..47482b9 100644
--- a/spec/propane/code_point_range_spec.rb
+++ b/spec/propane/code_point_range_spec.rb
@@ -54,10 +54,10 @@ class Propane
            CodePointRange.new(200, 300)])).to eq [
              CodePointRange.new(0, 59),
              CodePointRange.new(102, 199),
-             CodePointRange.new(301, 0xFFFFFFFF)]
+             CodePointRange.new(301, 0x7FFFFFFF)]
         expect(CodePointRange.invert_ranges(
           [CodePointRange.new(0, 500),
-           CodePointRange.new(7000, 0xFFFFFFFF)])).to eq [
+           CodePointRange.new(7000, 0x7FFFFFFF)])).to eq [
              CodePointRange.new(501, 6999)]
       end
     end