diff --git a/ext/nokogiri/extconf.rb b/ext/nokogiri/extconf.rb
index 26bb326fff0..6cd5fba066f 100644
--- a/ext/nokogiri/extconf.rb
+++ b/ext/nokogiri/extconf.rb
@@ -24,6 +24,10 @@ def openbsd?
   RbConfig::CONFIG['target_os'] =~ /openbsd/
 end
 
+def aix?
+  RbConfig::CONFIG["target_os"] =~ /aix/
+end
+
 def nix?
   ! (windows? || solaris? || darwin?)
 end
@@ -419,7 +423,7 @@ def using_system_libraries?
   $CFLAGS << " -DXP_WIN -DXP_WIN32 -DUSE_INCLUDED_VASPRINTF"
 end
 
-if solaris?
+if solaris? || aix?
   $CFLAGS << " -DUSE_INCLUDED_VASPRINTF"
 end