diff --git a/llvm/test/Analysis/lit.local.cfg b/llvm/test/Analysis/lit.local.cfg
new file mode 100644
--- /dev/null
+++ b/llvm/test/Analysis/lit.local.cfg
@@ -0,0 +1,8 @@
+# -*- Python -*- vim: set ft=python ts=4 sw=4 expandtab tw=79:
+from lit.llvm.subst import ToolSubst
+
+fc = ToolSubst('FileCheck', unresolved='fatal')
+# insert this first. Then, we'll first update the blank FileCheck command; then,
+# the default substitution of FileCheck will replace it to its full path.
+config.substitutions.insert(0, (fc.regex, 
+    'FileCheck --allow-unused-prefixes=false'))
diff --git a/llvm/test/lit.cfg.py b/llvm/test/lit.cfg.py
--- a/llvm/test/lit.cfg.py
+++ b/llvm/test/lit.cfg.py
@@ -82,6 +82,10 @@
         return ''
     return found_dylibs[0]
 
+# Define this first. Afterwards, use_default_substitutions will add the rule for
+# expanding FileCheck to the full path.
+config.substitutions.append(('%FileCheckWithUnusedPrefixes%', 
+    'FileCheck --allow-unused-prefixes=true'))
 
 llvm_config.use_default_substitutions()
 
@@ -90,7 +94,6 @@
 config.substitutions.append(('%shlibext', config.llvm_shlib_ext))
 config.substitutions.append(('%exeext', config.llvm_exe_ext))
 
-
 lli_args = []
 # The target triple used by default by lli is the process target triple (some
 # triple appropriate for generating code for the current process) but because