diff --git a/Lib/distutils/sysconfig.py b/Lib/distutils/sysconfig.py
index 37feae5..dab8a09 100644
--- a/Lib/distutils/sysconfig.py
+++ b/Lib/distutils/sysconfig.py
@@ -375,7 +375,10 @@ def parse_makefile(fn, g=None):
                     done[n] = item = ""
                 if found:
                     after = value[m.end():]
-                    value = value[:m.start()] + item + after
+                    value = value[:m.start()]
+                    if item.strip() not in value:
+                        value += item
+                    value += after
                     if "$" in after:
                         notdone[name] = value
                     else:
diff --git a/Lib/sysconfig.py b/Lib/sysconfig.py
index e3f79bf..bec4699 100644
--- a/Lib/sysconfig.py
+++ b/Lib/sysconfig.py
@@ -301,7 +301,10 @@ def _parse_makefile(filename, vars=None):
 
                 if found:
                     after = value[m.end():]
-                    value = value[:m.start()] + item + after
+                    value = value[:m.start()]
+                    if item.strip() not in value:
+                        value += item
+                    value += after
                     if "$" in after:
                         notdone[name] = value
                     else:
-- 
1.8.3.1