diff --git a/test/ruby_memcheck/ext/extconf_one.rb b/test/ruby_memcheck/ext/extconf_one.rb
index 5f48633..86e7a7b 100644
--- a/test/ruby_memcheck/ext/extconf_one.rb
+++ b/test/ruby_memcheck/ext/extconf_one.rb
@@ -2,6 +2,6 @@
 
 require "mkmf"
 
-$warnflags&.gsub!(/-Wdeclaration-after-statement/, "") # rubocop:disable Style/GlobalVars
+$warnflags&.gsub!("-Wdeclaration-after-statement", "") # rubocop:disable Style/GlobalVars
 
 create_makefile("ruby_memcheck_c_test_one")
diff --git a/test/ruby_memcheck/ext/extconf_two.rb b/test/ruby_memcheck/ext/extconf_two.rb
index 4d1ba8e..6b4a7ee 100644
--- a/test/ruby_memcheck/ext/extconf_two.rb
+++ b/test/ruby_memcheck/ext/extconf_two.rb
@@ -2,6 +2,6 @@
 
 require "mkmf"
 
-$warnflags&.gsub!(/-Wdeclaration-after-statement/, "") # rubocop:disable Style/GlobalVars
+$warnflags&.gsub!("-Wdeclaration-after-statement", "") # rubocop:disable Style/GlobalVars
 
 create_makefile("ruby_memcheck_c_test_two")