diff --git a/tools/configure b/tools/configure
index 666343d0a3..6db43ea30c 100755
--- a/tools/configure
+++ b/tools/configure
@@ -196,6 +196,8 @@ if [ "-" = "$extra_defines" ]; then
         extra_defines=""
      fi
   fi
+ else
+    extra_defines=""
  fi
 fi