diff --git a/test_common/CMakeLists.txt b/test_common/CMakeLists.txt
index 94efad73..b285d45d 100644
--- a/test_common/CMakeLists.txt
+++ b/test_common/CMakeLists.txt
@@ -4,7 +4,7 @@ set(HARNESS_COMMON_SOURCES
     harness/typeWrappers.cpp
     harness/mt19937.c
     harness/conversions.cpp
-    harness/rounding_mode.c
+    harness/rounding_mode.cpp
     harness/msvc9.c
 )
 
diff --git a/test_common/harness/rounding_mode.c b/test_common/harness/rounding_mode.cpp
similarity index 100%
rename from test_common/harness/rounding_mode.c
rename to test_common/harness/rounding_mode.cpp