diff --git a/auto/autoresearch.md b/auto/autoresearch.md
index 038491d2..6ec7e8b2 100644
--- a/auto/autoresearch.md
+++ b/auto/autoresearch.md
@@ -103,7 +103,7 @@ the sandbox.
 - cdc3438: For tag: migrate lax_parse to Cursor with zero-alloc scanning → allocs 29,620
 
 ## Current Best
-- **combined_µs**: ~4,500 (-39% from baseline)
-- **parse_µs**: ~3,200
-- **render_µs**: ~1,300
-- **allocations**: 29,620 (-53% from baseline)
+- **combined_µs**: ~4,100 (-44% from baseline)
+- **parse_µs**: ~2,900
+- **render_µs**: ~1,200
+- **allocations**: 25,535 (-59% from baseline)
diff --git a/lib/liquid/block_body.rb b/lib/liquid/block_body.rb
index 71331ef5..eb14aa2c 100644
--- a/lib/liquid/block_body.rb
+++ b/lib/liquid/block_body.rb
@@ -128,15 +128,10 @@ module Liquid
     PERCENT_BYTE = 37 # '%'.ord
 
     # Fast check if string is whitespace-only (replaces WhitespaceOrNothing regex)
+    BLANK_STRING_REGEX = /\A\s*\z/
+
     def self.blank_string?(str)
-      pos = 0
-      len = str.bytesize
-      while pos < len
-        b = str.getbyte(pos)
-        return false unless b == 32 || b == 9 || b == 10 || b == 13 || b == 12 # space, tab, \n, \r, \f
-        pos += 1
-      end
-      true
+      str.match?(BLANK_STRING_REGEX)
     end
 
     private def parse_for_document(tokenizer, parse_context, &block)