diff --git a/Modules/FindMPI.cmake b/Modules/FindMPI.cmake
index ad0172375..094f9e6c6 100644
--- a/Modules/FindMPI.cmake
+++ b/Modules/FindMPI.cmake
@@ -72,7 +72,7 @@
 # Microsoft HPC SDK is automatically added to the system path
 # Argonne National Labs MPICH2 sets a registry key that we can use.
 
-set(MPI_PACKAGE_DIR
+set(_MPI_PACKAGE_DIR
   mpi
   mpich
   openmpi
@@ -83,15 +83,15 @@ set(MPI_PACKAGE_DIR
   "Microsoft Compute Cluster Pack"
   )
 
-set(MPI_PREFIX_PATH)
+set(_MPI_PREFIX_PATH)
 if(WIN32)
-  list(APPEND MPI_PREFIX_PATH "[HKEY_LOCAL_MACHINE\\SOFTWARE\\MPICH\\SMPD;binary]/..")
+  list(APPEND _MPI_PREFIX_PATH "[HKEY_LOCAL_MACHINE\\SOFTWARE\\MPICH\\SMPD;binary]/..")
 endif()
 
 foreach(SystemPrefixDir ${CMAKE_SYSTEM_PREFIX_PATH})
-  foreach(MpiPackageDir ${MPI_PREFIX_PATH})
+  foreach(MpiPackageDir ${_MPI_PREFIX_PATH})
     if(EXISTS ${SystemPrefixDir}/${MpiPackageDir})
-      list(APPEND MPI_PREFIX_PATH "${SystemPrefixDir}/${MpiPackageDir}")
+      list(APPEND _MPI_PREFIX_PATH "${SystemPrefixDir}/${MpiPackageDir}")
     endif()
   endforeach(MpiPackageDir)
 endforeach(SystemPrefixDir)
@@ -99,7 +99,7 @@ endforeach(SystemPrefixDir)
 # Most mpi distros have some form of mpiexec which gives us something we can reliably look for.
 find_program(MPIEXEC
   NAMES mpiexec mpirun lamexec
-  PATHS ${MPI_PREFIX_PATH}
+  PATHS ${_MPI_PREFIX_PATH}
   PATH_SUFFIXES bin
   DOC "Executable for running MPI programs."
   )
@@ -222,7 +222,7 @@ elseif (MPI_COMPILE_CMDLINE)
     # If all else fails, just search for mpi.h in the normal include
     # paths.
     find_path(MPI_INCLUDE_PATH mpi.h
-  HINTS ${_MPI_BASE_DIR} ${MPI_PREFIX_PATH}
+  HINTS ${_MPI_BASE_DIR} ${_MPI_PREFIX_PATH}
   PATH_SUFFIXES include
     )
     set(MPI_INCLUDE_PATH_WORK ${MPI_INCLUDE_PATH})
@@ -304,7 +304,7 @@ elseif (MPI_COMPILE_CMDLINE)
 else (MPI_COMPILE_CMDLINE)
 # No MPI compiler to interogate so attempt to find everything with find functions.
   find_path(MPI_INCLUDE_PATH mpi.h
-    HINTS ${_MPI_BASE_DIR} ${MPI_PREFIX_PATH}
+    HINTS ${_MPI_BASE_DIR} ${_MPI_PREFIX_PATH}
     PATH_SUFFIXES include
     )
 
@@ -317,13 +317,13 @@ else (MPI_COMPILE_CMDLINE)
 
   find_library(MPI_LIBRARY
     NAMES mpi mpich msmpi
-    HINTS ${_MPI_BASE_DIR} ${MPI_PREFIX_PATH}
+    HINTS ${_MPI_BASE_DIR} ${_MPI_PREFIX_PATH}
     PATH_SUFFIXES lib lib/${MS_MPI_ARCH_DIR} Lib Lib/${MS_MPI_ARCH_DIR}
     )
 
   find_library(MPI_EXTRA_LIBRARY
     NAMES mpi++
-    HINTS ${_MPI_BASE_DIR} ${MPI_PREFIX_PATH}
+    HINTS ${_MPI_BASE_DIR} ${_MPI_PREFIX_PATH}
     PATH_SUFFIXES lib
     DOC "Extra MPI libraries to link against.")
 
@@ -358,6 +358,6 @@ mark_as_advanced(MPI_INCLUDE_PATH MPI_COMPILE_FLAGS MPI_LINK_FLAGS MPI_LIBRARY
   MPI_EXTRA_LIBRARY)
 
 # unset to cleanup namespace
-unset(MPI_PACKAGE_DIR)
-unset(MPI_PREFIX_PATH)
+unset(_MPI_PACKAGE_DIR)
+unset(_MPI_PREFIX_PATH)
 unset(_MPI_BASE_DIR)