diff --git a/lib/CMakeLists.txt b/lib/CMakeLists.txt
index f20873cdbf..2b601673a2 100644
--- a/lib/CMakeLists.txt
+++ b/lib/CMakeLists.txt
@@ -47,7 +47,7 @@ if(CURL_BUILD_TESTING)
   target_link_libraries(curlu PUBLIC ${CURL_LIBS})
   # There is plenty of parallelism when building the testdeps target.
   # Override the curlu batch size with the maximum to optimize performance.
-  set_target_properties(curlu PROPERTIES UNITY_BUILD_BATCH_SIZE 0 C_CLANG_TIDY "")
+  set_target_properties(curlu PROPERTIES UNITY_BUILD ON UNITY_BUILD_BATCH_SIZE 0 C_CLANG_TIDY "")
 
   add_custom_command(OUTPUT "${CMAKE_CURRENT_BINARY_DIR}/unitprotos.h"
     WORKING_DIRECTORY "${CMAKE_CURRENT_SOURCE_DIR}"
diff --git a/src/CMakeLists.txt b/src/CMakeLists.txt
index 0063b438c2..87c26e30d1 100644
--- a/src/CMakeLists.txt
+++ b/src/CMakeLists.txt
@@ -116,7 +116,7 @@ set_target_properties(curlinfo PROPERTIES UNITY_BUILD OFF)
 add_library(curltool STATIC EXCLUDE_FROM_ALL ${CURL_CFILES} ${CURL_HFILES} ${_curlx_cfiles_lib} ${_curlx_hfiles_lib})
 target_compile_definitions(curltool PUBLIC "CURL_STATICLIB" "UNITTESTS")
 target_link_libraries(curltool PUBLIC ${CURL_LIBS})
-set_target_properties(curltool PROPERTIES C_CLANG_TIDY "")
+set_target_properties(curltool PROPERTIES UNITY_BUILD ON C_CLANG_TIDY "")
 
 if(CURL_HAS_LTO)
   set_target_properties(${EXE_NAME} PROPERTIES INTERPROCEDURAL_OPTIMIZATION TRUE)