diff --git a/.travis.yml b/.travis.yml
index cc7e12d9..9df75c61 100644
--- a/.travis.yml
+++ b/.travis.yml
@@ -1,5 +1,6 @@
 language: ruby
 rvm:
+  - 2.4.10
   - 2.5.8
   - 2.6.6
   - 2.7.1
diff --git a/ext/ruby_prof/extconf.rb b/ext/ruby_prof/extconf.rb
index 8c461b9b..6dd5bf7d 100644
--- a/ext/ruby_prof/extconf.rb
+++ b/ext/ruby_prof/extconf.rb
@@ -3,4 +3,7 @@
 # This function was added in Ruby 2.5, so once Ruby 2.4 is no longer supported this can be removed
 have_func('rb_tracearg_callee_id', ["ruby.h"])
 
+# We want to intermix declarations and code (ie, don't define all variables at the top of the method)
+$CFLAGS += ' -std=c99'
+
 create_makefile("ruby_prof")