diff --git a/tests/CMakeLists.txt b/tests/CMakeLists.txt
index d452017..72679db 100644
--- a/tests/CMakeLists.txt
+++ b/tests/CMakeLists.txt
@@ -52,3 +52,8 @@ target_link_libraries(
 
 endforeach(TESTNAME)
 
+# Make sure NDEBUG is always undefined for tests
+if (UNIX OR MINGW OR CYGWIN)
+    list(APPEND CMAKE_C_FLAGS -UNDEBUG)
+endif()
+