diff --git a/au/CMakeLists.txt b/au/CMakeLists.txt
index 770f4372..7b237dc0 100644
--- a/au/CMakeLists.txt
+++ b/au/CMakeLists.txt
@@ -101,6 +101,8 @@ header_only_library(
     unit_of_measure
     unit_symbol
   GTEST_SRCS
+    prefix_test.cc
+  GTEST_EXTRA_DEPS
     testing
 )