diff --git a/test/lib/llvm.exp b/test/lib/llvm.exp
index ab7c994948a..160a7848e39 100644
--- a/test/lib/llvm.exp
+++ b/test/lib/llvm.exp
@@ -68,6 +68,8 @@ proc substitute { line test tmpFile } {
   regsub -all {%s} $new_line $test new_line
   #replace %t with temp filenames
   regsub -all {%t} $new_line [file join Output $tmpFile] new_line
+  #replace %% with %
+  regsub -all {%%} $new_line % new_line
   return $new_line
 }