diff --git a/include/CMakeLists.txt b/include/CMakeLists.txt
index 985a353..3081b26 100644
--- a/include/CMakeLists.txt
+++ b/include/CMakeLists.txt
@@ -9,3 +9,9 @@
         PERMISSIONS OWNER_READ OWNER_WRITE GROUP_READ WORLD_READ)
 
 endif(INSTALL_MBEDTLS_HEADERS)
+
+# Make scripts and data files needed for testing available in an
+# out-of-source build.
+if (NOT ${CMAKE_CURRENT_BINARY_DIR} STREQUAL ${CMAKE_CURRENT_SOURCE_DIR})
+    link_to_source(mbedtls)
+endif()