diff -r 642247a536d5 Tools/clinic/clinic.py
--- a/Tools/clinic/clinic.py	Sat Mar 14 20:17:38 2015 -0700
+++ b/Tools/clinic/clinic.py	Sat Mar 14 21:18:36 2015 -0700
@@ -820,7 +820,8 @@
             cpp_if = "#if " + conditional
             cpp_endif = "#endif /* " + conditional + " */"
 
-            if methoddef_define:
+            if methoddef_define and f.name not in clinic.ifndef_symbols:
+                clinic.ifndef_symbols.add(f.name)
                 methoddef_ifndef = normalize_snippet("""
                     #ifndef {methoddef_name}
                         #define {methoddef_name}
@@ -1574,6 +1575,7 @@
         ))
 
         self.field_destinations_stack = []
+        self.ifndef_symbols = set()
 
         self.presets = {}
         preset = None