diff --git a/cmake/HandleMetis.cmake b/cmake/HandleMetis.cmake
index 9c29e5776..5cbec4ff5 100644
--- a/cmake/HandleMetis.cmake
+++ b/cmake/HandleMetis.cmake
@@ -21,7 +21,12 @@ if(GTSAM_USE_SYSTEM_METIS)
     mark_as_advanced(METIS_LIBRARY)
 
     add_library(metis-gtsam-if INTERFACE)
-    target_include_directories(metis-gtsam-if BEFORE INTERFACE ${METIS_INCLUDE_DIR})
+    target_include_directories(metis-gtsam-if BEFORE INTERFACE ${METIS_INCLUDE_DIR}
+      # gtsam_unstable/partition/FindSeparator-inl.h uses internal metislib.h API
+      # via extern "C"
+      $<BUILD_INTERFACE:${GTSAM_SOURCE_DIR}/gtsam/3rdparty/metis/libmetis>
+      $<BUILD_INTERFACE:${GTSAM_SOURCE_DIR}/gtsam/3rdparty/metis/GKlib>
+    )
     target_link_libraries(metis-gtsam-if INTERFACE ${METIS_LIBRARY})
   endif()
 else()
@@ -30,10 +35,12 @@ else()
   add_subdirectory(${GTSAM_SOURCE_DIR}/gtsam/3rdparty/metis)
 
   target_include_directories(metis-gtsam BEFORE PUBLIC
+    $<INSTALL_INTERFACE:include/gtsam/3rdparty/metis/>
     $<BUILD_INTERFACE:${GTSAM_SOURCE_DIR}/gtsam/3rdparty/metis/include>
+    # gtsam_unstable/partition/FindSeparator-inl.h uses internal metislib.h API
+    # via extern "C"
     $<BUILD_INTERFACE:${GTSAM_SOURCE_DIR}/gtsam/3rdparty/metis/libmetis>
     $<BUILD_INTERFACE:${GTSAM_SOURCE_DIR}/gtsam/3rdparty/metis/GKlib>
-    $<INSTALL_INTERFACE:include/gtsam/3rdparty/metis/>
   )
 
   add_library(metis-gtsam-if INTERFACE)
diff --git a/gtsam/inference/Ordering.cpp b/gtsam/inference/Ordering.cpp
index 440d2b828..2ac2c0dde 100644
--- a/gtsam/inference/Ordering.cpp
+++ b/gtsam/inference/Ordering.cpp
@@ -25,11 +25,7 @@
 #include <gtsam/3rdparty/CCOLAMD/Include/ccolamd.h>
 
 #ifdef GTSAM_SUPPORT_NESTED_DISSECTION
-#ifdef GTSAM_USE_SYSTEM_METIS
 #include <metis.h>
-#else
-#include <gtsam/3rdparty/metis/include/metis.h>
-#endif
 #endif
 
 using namespace std;
diff --git a/gtsam_unstable/partition/FindSeparator-inl.h b/gtsam_unstable/partition/FindSeparator-inl.h
index 2e48b0d45..0e4950b79 100644
--- a/gtsam_unstable/partition/FindSeparator-inl.h
+++ b/gtsam_unstable/partition/FindSeparator-inl.h
@@ -20,11 +20,10 @@
 
 #include "FindSeparator.h"
 
-#ifndef GTSAM_USE_SYSTEM_METIS
+#include <metis.h>
 
 extern "C" {
-#include <metis.h>
-#include "metislib.h"
+#include <metislib.h>
 }
 
 
@@ -566,5 +565,3 @@ namespace gtsam { namespace partition {
   }
 
 }} //namespace
-
-#endif
diff --git a/gtsam_unstable/partition/tests/testFindSeparator.cpp b/gtsam_unstable/partition/tests/testFindSeparator.cpp
index 63acc8f18..fe49de928 100644
--- a/gtsam_unstable/partition/tests/testFindSeparator.cpp
+++ b/gtsam_unstable/partition/tests/testFindSeparator.cpp
@@ -20,8 +20,6 @@ using namespace std;
 using namespace gtsam;
 using namespace gtsam::partition;
 
-#ifndef GTSAM_USE_SYSTEM_METIS
-
 /* ************************************************************************* */
 // x0 - x1 - x2
 // l3        l4
@@ -229,8 +227,6 @@ TEST ( Partition, findSeparator3_with_reduced_camera )
   LONGS_EQUAL(2, partitionTable[28]);
 }
 
-#endif
-
 /* ************************************************************************* */
 int main() { TestResult tr; return TestRegistry::runAllTests(tr);}
 /* ************************************************************************* */