diff --git a/Rakefile b/Rakefile

index 8c9487436..1487cc237 100644

--- a/Rakefile

+++ b/Rakefile

@@ -355,7 +355,7 @@ cxx_compiler = lambda do |*args|

     # Even -O1 causes compilation time & memory usage to skyrocket,

     # possibly exponentially, with the number of entries to

     # emplace_back() into the vector.

-    flags.gsub!(%r{ -O\d+ }, ' -O0 ')

+    flags.gsub!(%r{-O\d+}, '-O0')

   end

   args = [