diff --git a/modules/definitions.cmake b/modules/definitions.cmake
new file mode 100644
index 0000000..0ba9e3d
--- /dev/null
+++ b/modules/definitions.cmake
@@ -0,0 +1,16 @@
+#.rst:
+#
+# Add preprocessor definitions.
+#
+# Variables used::
+#
+#   PREPROCESSOR_DEFINITIONS
+#
+# autocmake.cfg configuration::
+#
+#   docopt: --add-definitions=<STRING> Add preprocesor definitions [default: ''].
+#   define: '-DPREPROCESSOR_DEFINITIONS="%s"' % arguments['--add-definitions']
+
+if(NOT "${PREPROCESSOR_DEFINITIONS}" STREQUAL "")
+    add_definitions(${PREPROCESSOR_DEFINITIONS})
+endif()