diff --git a/lib/parser/lexer/literal.rb b/lib/parser/lexer/literal.rb
index de906a7f9..b477a244f 100644
--- a/lib/parser/lexer/literal.rb
+++ b/lib/parser/lexer/literal.rb
@@ -247,7 +247,7 @@ def delimiter?(delimiter)
         # E
         # because there are not enough leading spaces in the closing delimiter.
         delimiter.end_with?(@end_delim) &&
-          delimiter.delete_suffix(@end_delim).bytes.all? { |c| c == SPACE }
+          delimiter.sub(/#{@end_delim}\z/, '').bytes.all? { |c| c == SPACE }
       elsif @indent
         @end_delim == delimiter.lstrip
       else
diff --git a/parser.gemspec b/parser.gemspec
index 909e5d9d6..3c5bd3ec8 100644
--- a/parser.gemspec
+++ b/parser.gemspec
@@ -24,7 +24,7 @@ Gem::Specification.new do |spec|
   spec.executables   = spec.files.grep(%r{^bin/}) { |f| File.basename(f) }
   spec.require_paths = ['lib']
 
-  spec.required_ruby_version = '>= 2.5.0'
+  spec.required_ruby_version = '>= 2.0.0'
 
   spec.add_dependency             'ast',       '~> 2.4.1'
   spec.add_dependency             'racc'