diff --git a/ChemistryLib/CMakeLists.txt b/ChemistryLib/CMakeLists.txt
index 12ccb9b2e20facac633e6679ecce9c9456fe612b..77d2b40bb3a60e320651757394aa18f227e3b048 100644
--- a/ChemistryLib/CMakeLists.txt
+++ b/ChemistryLib/CMakeLists.txt
@@ -11,3 +11,6 @@ include(GenerateExportHeader)
 generate_export_header(ChemistryLib)
 
 target_link_libraries(ChemistryLib PUBLIC iphreeqc PRIVATE NumLib spdlog::spdlog)
+
+# See https://github.com/ufz/ogs/pull/2982#issuecomment-641086788
+set_source_files_properties(PhreeqcIO.cpp PROPERTIES SKIP_UNITY_BUILD_INCLUSION TRUE)