diff --git a/CMakeLists.txt b/CMakeLists.txt
index 62d411e9..956c82f2 100644
--- a/CMakeLists.txt
+++ b/CMakeLists.txt
@@ -88,7 +88,10 @@ endif()
 # OPENSSL_ROOT_DIR=/usr/local/opt/openssl cmake ..
 include_directories(
     ${GFLAGS_INCLUDE_DIRS} ${GLOG_INCLUDE_DIRS} ${OPENSSL_INCLUDE_DIR}
-    ${Python3_INCLUDE_DIRS})
+)
+if (${Python3_FOUND})
+    include_directories(${Python3_INCLUDE_DIRS})
+endif()
 include_directories(src)
 
 add_library(s2
@@ -200,10 +203,12 @@ add_library(s2
             src/s2/util/math/exactfloat/exactfloat.cc
             src/s2/util/math/mathutil.cc
             src/s2/util/units/length-units.cc)
+if (GTEST_ROOT)
 add_library(s2testing STATIC
             src/s2/s2builderutil_testing.cc
             src/s2/s2shapeutil_testing.cc
             src/s2/s2testing.cc)
+endif()
 target_link_libraries(
     s2
     ${GFLAGS_LIBRARIES} ${GLOG_LIBRARIES} ${OPENSSL_LIBRARIES}
@@ -414,7 +419,11 @@ install(FILES src/s2/util/math/mathutil.h
 install(FILES src/s2/util/units/length-units.h
               src/s2/util/units/physical-units.h
         DESTINATION include/s2/util/units)
+if (GTEST_ROOT)
 install(TARGETS s2 s2testing DESTINATION lib)
+else()
+install(TARGETS s2 DESTINATION lib)
+endif()
 
 message("GTEST_ROOT: ${GTEST_ROOT}")
 if (GTEST_ROOT)