diff --git a/src/libmongoc/CMakeLists.txt b/src/libmongoc/CMakeLists.txt
index d09d706..5d84225 100644
--- a/src/libmongoc/CMakeLists.txt
+++ b/src/libmongoc/CMakeLists.txt
@@ -109,7 +109,9 @@ if (NOT ENABLE_SSL STREQUAL OFF)
       if (LIBRESSL_FOUND)
          message ("--   Found ${LIBRESSL_LIBRARIES}")
          set (SSL_LIBRARIES ${LIBRESSL_LIBRARIES})
-         include_directories ("${LIBRESSL_INCLUDE_DIRS}")
+         if (${LIBRESSL_INCLUDE_DIRS})
+           include_directories ("${LIBRESSL_INCLUDE_DIRS}")
+         endif ()
          link_directories ("${LIBRESSL_LIBRARY_DIRS}")
          set (LIBRESSL 1)
       else ()